Document semantic linefeeds in CONTRIBUTING.rst (#500)

CONTRIBUTING.rst

@@ -3,8 +3,7 @@ Contributing to Towncrier
 
 Want to contribute to this project? Great! We'd love to hear from you!
 
-As a developer and user, you probably have some questions about our
-project and how to contribute.
+As a developer and user, you probably have some questions about our project and how to contribute.
 In this article, we try to answer these and give you some recommendations.
 
 
@@ -36,8 +35,7 @@ There are several options to contribute to this project:
 
 * Modify the code.
 
-  If you would love to see the new feature in the next release, this is
-  probably the best way.
+  If you would love to see the new feature in the next release, this is probably the best way.
 
 
 Modifying the code
@@ -58,7 +56,6 @@ We recommend the following workflow:
 
    $ git clone [email protected]:GITHUB_USER/towncrier.git
 
-
 #. Prepare a pull request:
 
    a. Create a new branch with::
@@ -68,10 +65,11 @@ We recommend the following workflow:
    b. Write your test cases and run the complete test suite, see the section
       *Running the test suite* for details.
 
-
    c. Document any user-facing changes in one of the ``/docs/`` files.
+      Please use `one sentence per line`_.
 
    d. Create a newsfragment in ``src/towncrier/newsfragments/`` describing the changes and containing information that is of interest to end-users.
+      Please use `one sentence per line`_ here, too.
 
    e. Create a `pull request`_.
       Describe in the pull request what you did and why.
@@ -147,4 +145,5 @@ fails with our dummy test commits.
 .. _issues:  https://github.com/twisted/towncrier/issues
 .. _pull request: https://github.com/twisted/towncrier/pulls
 .. _nox: https://nox.thea.codes/
+.. _`one sentence per line`: https://rhodesmill.org/brandon/2012/one-sentence-per-line/
 .. _twisted.trial: https://github.com/twisted/trac-wiki-archive/blob/trunk/TwistedTrial.mediawiki