CONTRIBUTING.rst: Improve commit guidelines

Few words about the commit's titles were added (capital letter).

CONTRIBUTING.rst

@@ -52,10 +52,11 @@ Commit Guidelines
  - Make sure commit titles are always in present tense, and are not
    followed by punctuation.
 
- - Prefix commit titles with the module name, followed by a colon and a
-   space (unless modifying a file in the base directory).  When
-   modifying cmake modules, prefix with "cmake".  So for example, if you
-   are modifying the obs-ffmpeg plugin::
+ - Prefix each commit's titles with the module name, followed by a colon
+   and a space (unless modifying a file in the base directory).  After
+   that, the first word should be capitalized.
+
+   So for example, if you are modifying the obs-ffmpeg plugin::
 
      obs-ffmpeg: Fix bug with audio output
 
@@ -63,4 +64,6 @@ Commit Guidelines
 
      libobs: Fix source not displaying
 
+   Note: When modifying cmake modules, just prefix with "cmake".
+
  - If you still need examples, please view the commit history.