doc: contributing: add TOC

CONTRIBUTING.md

@@ -1,8 +1,9 @@
 <!-- consolidating dev docs from wiki, https://github.com/simonmichael/hledger/issues/920 WIP -->
+$toc$
 
 # Contributor Guide
 
-<!-- $ toc -->
+<br clear=all>
 
 ## Quick Links
 

Shake.hs

@@ -281,7 +281,8 @@ main = do
           "--lua-filter tools/pandoc-demote-headers.lua"
           ">>" webmancombined :: Action ExitCode
 
-    -- Copy some extra markdown files from the main repo into the site.
+    -- Copy some extra markdown files from the main repo into the site
+    -- TODO adding table of contents placeholders
     ["site/README.md", "site/CONTRIBUTING.md"]  |%> \out ->
       copyFile' (dropDirectory1 out) out -- XXX (map toLower out)