Add missing docstrings

patacrep/songs/__init__.py

@@ -195,6 +195,7 @@ class Song:
         raise NotImplementedError()
 
     def get_cover_fullpath(self, default=None):
+        """Return the fullpath of the cover file if found"""
         filename = self.data.get('cov')
         if not filename:
             return default

patacrep/songs/chordpro/ast.py

@@ -40,6 +40,7 @@ class OrderedLifoDict:
         return self._values[key]
 
     def get(self, key, default=None):
+        """Same as :meth:`dict.get`."""
         return self._values.get(key, default)
 
 def _indent(string):