docs: mention C libs in the cabal install instructions

INSTALL.md

@@ -40,7 +40,15 @@ use the troubleshooting tips below if needed.
 
 Ensure you have [GHC](http://hackage.haskell.org/ghc/) or
 the [Haskell Platform](http://hackage.haskell.org/platform/) installed.
-hledger currently requires GHC 7.2 or greater, and hledger-web requires GHC 7.4 or greater.
+hledger requires GHC 7.2 or greater, and hledger-web requires GHC 7.4 or greater.
+
+Also note that some Haskell packages depend on C packages, and cabal
+currently isn't able to install or identify those for you. A common
+issue is not having all the ncurses C libraries installed. A quick way
+to ensure you have all required C libs is to
+[install hledger once with your system package manager](#install-with-your-system-package-manager)
+before installing the latest version with cabal.
+
 Then install the hledger command-line tool:
 
     $ cabal update
@@ -77,7 +85,9 @@ To download and build the latest development version of hledger, ensure you have
     $ cd hledger
     $ cabal update
     $ cabal install ./hledger-lib ./hledger [./hledger-web]
-    
+
+The same [notes about C libs etc.](#install-from-hackage-with-cabal) apply.
+
 ## Troubleshooting
 
 There are a lot of ways things can go wrong. Here are
@@ -92,7 +102,7 @@ you. Tip: blindly reinstalling/upgrading everything in sight probably
 won't work, it's better to go in small steps and understand the problem,
 or get help.
 
-#. **hledger not found ?**  
+#. **hledger not found ?**
   If cabal install succeeded but you get a message like "hledger not found" when you run hledger,
   you should add cabal's bin directory to your PATH environment variable.
   Eg on unix-like systems, something like:
@@ -100,30 +110,30 @@ or get help.
         $ echo 'export PATH=$PATH:~/cabal/bin' >> ~/.bash_profile
         $ source ~/.bash_profile
 
-#. **Did you cabal update ?**  
+#. **Did you cabal update ?**
   If not, `cabal update` and try again.
 
-#. **Do you have a new enough version of GHC ?**  
+#. **Do you have a new enough version of GHC ?**
   Run `ghc --version`. hledger requires GHC 7.0 or greater
   (on [some platforms](#5551), 7.2.1 can be helpful).
 
-#. **Do you have a new enough version of cabal ?**  
+#. **Do you have a new enough version of cabal ?**
   Avoid ancient versions.  `cabal --version` should report at least
   0.10 (and 0.14 is much better). You may be able to upgrade it with:
-  
+
         $ cabal update
         $ cabal install cabal-install-0.14
 
-#. **Are your installed GHC/cabal packages in good repair ?**  
+#. **Are your installed GHC/cabal packages in good repair ?**
   Run `ghc-pkg check`. If it reports problems, some of your packages have
-  become inconsistent, and you should fix these first. 
+  become inconsistent, and you should fix these first.
   [ghc-pkg-clean](https://gist.github.com/1185421) is an easy way.
 
-#. <a name="cabaldeps" />**cabal can't satisfy the new dependencies due to old installed packages**  
+#. <a name="cabaldeps" />**cabal can't satisfy the new dependencies due to old installed packages**
   Cabal dependency failures become more likely as you install more
   packages over time. If `cabal install hledger-web --dry` says it can't
   satisfy dependencies, you have this problem. You can:
-  
+
     a. try to understand which packages to remove (with `ghc-pkg unregister`)
        or which constraints to add (with `--constraint 'PKG == ...'`) to help cabal
        find a solution
@@ -135,7 +145,7 @@ or get help.
     c. or (easiest) erase your installed packages with
        [ghc-pkg-reset](https://gist.github.com/1185421) and try again.
 
-#. **Dependency or compilation error in one of the new packages ?**  
+#. **Dependency or compilation error in one of the new packages ?**
    If cabal starts downloading and building packages and then terminates
    with an error, look at the output carefully and identify the problem
    package(s).  If necessary, add `-v2` or `-v3` for more verbose
@@ -149,7 +159,7 @@ or get help.
    [recent commits](http://github.com/simonmichael/hledger/commits) to
    see if the [latest development version](#installing) might have a fix.
 
-#. **ExitFailure 11**  
+#. **ExitFailure 11**
   See
   [http://hackage.haskell.org/trac/hackage/ticket/777](http://hackage.haskell.org/trac/hackage/ticket/777).
   This means that a build process has been killed, usually because it grew
@@ -158,11 +168,11 @@ or get help.
   or limit GHC's heap size by doing `cabal install ... --ghc-options='+RTS
   -M400m'` (400 megabytes works well on my 1G VPS, adjust up or down..)
 
-#. <a name="5551" />**Can't load .so/.DLL for: ncursesw (/usr/lib/libncursesw.so: file too short)**  
+#. <a name="5551" />**Can't load .so/.DLL for: ncursesw (/usr/lib/libncursesw.so: file too short)**
   (or similar): cf [GHC bug #5551](http://hackage.haskell.org/trac/ghc/ticket/5551).
   Upgrade GHC to 7.2.1, or try your luck with [this workaround](http://eclipsefp.github.com/faq.html).
 
-#. <a name="iconv" />**Undefined iconv symbols on OS X**  
+#. <a name="iconv" />**Undefined iconv symbols on OS X**
    This kind of error:
 
         Linking dist/build/hledger/hledger ...
@@ -181,13 +191,12 @@ or get help.
         $ cabal install hledger --extra-lib-dirs=/usr/lib
 
     or permanently, add this to ~/.cabal/config:
-    
+
         extra-lib-dirs: /usr/lib
 
-#. **hledger-vty requires curses-related libraries**  
+#. **hledger-vty requires curses-related libraries**
   On Ubuntu, eg, you'll need the `libncurses5-dev` package. On Windows,
   these are not available (unless perhaps via Cygwin.)
 
-#. **hledger-chart requires GTK-related libraries**  
+#. **hledger-chart requires GTK-related libraries**
   On Ubuntu, eg, install the `libghc6-gtk-dev` package. See also [Gtk2Hs installation notes](http://code.haskell.org/gtk2hs/INSTALL).
-