doc: add contributors page to site, lower-case it

doc/developer-guide.md

@@ -435,7 +435,7 @@ If you're new to this process, [help.github.com](http://help.github.com) may be
 
 ### Become a contributor
 
-- after getting one or more patches committed, read and sign the [contributor list & agreement](CONTRIBUTORS.html)
+- after getting one or more patches committed, read and sign the [contributor list & agreement](contributors.html)
 - or, [ask](#how-to-get-help) to be added
 
 ### Do code review

doc/site/contributors.md

@@ -0,0 +1 @@
+../contributors.md

doc/site/index.md

@@ -10,7 +10,7 @@ and a [Haskell library](http://hackage.haskell.org/package/hledger-lib) for
 building your own programs and [scripts](more-docs.html#scripting-examples)
 (hledger is written in Haskell).
 hledger is free software, available under the GNU GPLv3+,
-created by [Simon Michael](http://joyful.com) and [contributors](CONTRIBUTORS.html).
+created by [Simon Michael](http://joyful.com) and [contributors](contributors.html).
 
 Though limited in features, hledger is lightweight, usable and reliable.
 For some, it is a simple, flexible, future-proof alternative to Quicken or GnuCash.