obsolete: add a note that explains creating aliases for marker flags

mercurial/obsolete.py

@@ -148,6 +148,8 b' def isenabled(repo, option):'
 
     return _getoptionvalue(repo, option)
 
+# Creating aliases for marker flags because evolve extension looks for
+# bumpedfix in obsolete.py
 bumpedfix = obsutil.bumpedfix
 usingsha256 = obsutil.usingsha256