Add comment to walrus operator

Author: james-bruten-mo

bdiff/git_bdiff.py

@@ -63,6 +63,8 @@ def get_branch_name(self):
         """Get the name of the current branch."""
         result = None
         for line in self.run_git(["branch", "--show-current"]):
+            # Set m to self._branch_pattern result
+            # Then check m evaluates to True
             if m := self._branch_pattern.match(line):
                 result = m.group(1)
                 break