Introduce changelog metadata in commit messages

Add Contribution section into README, including the guidelines for
adding changelog metadata to the commit messages. Thanks to this,
changelog can be automatically generated while staying useful.

Author: pkratoch

.git-commit-template

@@ -0,0 +1,16 @@
+
+
+# In addition to regular commit message, you can uncomment and fill in the
+# following to include this change in the released RPM package changelog:
+
+# = changelog =
+# msg:
+# type:
+# resolves:
+# related:
+
+# msg        = message to be included in the changelog
+# type       = one of: bugfix/enhancement/security
+# resolves   = URLs to bugs or issues resolved by this commit
+# related    = URLs to any related bugs or issues
+

README.md

@@ -114,6 +114,36 @@ Example of run only one specific test: ``PYTHONPATH=`readlink -f ./build/librepo
 
     PYTHONPATH=`readlink -f ./build/librepo/python/python3/` nosetests-3.3 -s -v tests/python/tests/
 
+## Contribution
+
+Here's the most direct way to get your work merged into the project.
+
+1. Fork the project
+1. Clone down your fork
+1. Implement your feature or bug fix and commit changes
+1. If the change fixes a bug at [Red Hat bugzilla](https://bugzilla.redhat.com/), or if it is important to the end user, add the following block to the commit message:
+    
+       = changelog =
+       msg:           message to be included in the changelog
+       type:          one of: bugfix/enhancement/security (this field is required when message is present)
+       resolves:      URLs to bugs or issues resolved by this commit (can be specified multiple times)
+       related:       URLs to any related bugs or issues (can be specified multiple times)
+
+   * For example::
+
+         = changelog =
+         msg: Decode package URL when using for local filename
+         type: bugfix
+         resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1817130
+
+   * For your convenience, you can also use git commit template by running the following command in the top-level directory of this project:
+
+         git config commit.template ./.git-commit-template
+
+1. In a separate commit, add your name into the [authors file](https://github.com/rpm-software-management/librepo/blob/master/AUTHORS) as a reward for your generosity
+1. Push the branch to your fork
+1. Send a pull request for your branch
+
 ## Links
 
 * [Red Hat Bugzilla](https://bugzilla.redhat.com/buglist.cgi?query_format=advanced&bug_status=NEW&bug_status=ASSIGNED&bug_status=MODIFIED&bug_status=VERIFIED&component=librepo)