Clarify the identifier naming rules

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@15285 a1c6a512-1295-4272-9138-f99709370657
diff --git a/docs/CONTRIBUTING b/docs/CONTRIBUTING
index d36e359..e426770 100644
--- a/docs/CONTRIBUTING
+++ b/docs/CONTRIBUTING
@@ -28,10 +28,12 @@
 Write normal C code. Don't redefine the language. No new types (structs are
 structs, not typedefs), no C++isms or Javaisms.
 
-Names
+Identifiers
 -----
+We do not want mixed case identifiers.
 Variables and function names should be all lower case.
-Preprocessor symbols should be all uppercase.
+Struct and enum names should be all lower case.
+Preprocessor symbols and enum constants should be all upper case.
 
 Comments
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