doc: add contributing guide

Author: awwpotato

CONTRIBUTING.md

@@ -675,6 +675,7 @@ stdenvNoCC.mkDerivation {
     ${writePages}
     cat $renderedSummaryPath >>src/SUMMARY.md
     cp ${../README.md} src/README.md
+    cp ${../CONTRIBUTING.md} src/contributing.md
     cp ${../gnome.png} src/gnome.png
     cp ${../kde.png} src/kde.png
   '';

doc/default.nix

@@ -1,19 +1,13 @@
 [Introduction](README.md)
 
+[Contributing guide](contributing.md)
+
 # User guide
 
 - [Installation](installation.md)
 - [Configuration](configuration.md)
 - [Tips and tricks](tricks.md)
 
-# Contributing
-
-- [Commit Convention](commit_convention.md)
-- [Development Environment](development_environment.md)
-- [Adding modules](modules.md)
-- [Testbeds](testbeds.md)
-- [Style guide](styling.md)
-
 # Reference
 
 <!--