Improve the rationale for commit message style

Author: patiencedaur

doc/contributing/docs/git.rst

@@ -38,12 +38,12 @@ If your PR closes more than one issue, add such a line for each issue.
 Commit messages
 ---------------
 
-*   In your commit message, convey the nature of the change and possibly the reason why it was made.
+*   In your commit message, explain the reason why you made the changes. It often cannot be deduced from the changes themselves.
 *   Don't specify the files you've changed or the issue you're working on.
     The file names can be looked up in the "Files" section of the PR, and the PR description has the issue number(s).
 *   Use the imperative mood.
 *   Start with a capital letter, don't add ending punctuation.
-*   Try to stick to 50 characters or so.
+*   Try to stick to 50 characters or less.
 *   (Optional) Use the telegraphic style, or "headlinese", dropping the articles.
 
 Good examples