patman: Update Commit to include the message

There is in fact a 'msg' member for Commit, set up by the
Patchstream._close_commit() function. Declare it in the docs and set it
to empty when the Commit is created.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

tools/patman/commit.py

@@ -17,6 +17,7 @@ class Commit:
     Variables:
         hash: Commit hash
         subject: Subject line
+        msg: Commit message body (everything after the subject line)
         tags: List of maintainer tag strings
         changes: Dict containing a list of changes (single line strings).
             The dict is indexed by change version (an integer)
@@ -35,6 +36,7 @@ class Commit:
     def __init__(self, hash):
         self.hash = hash
         self.subject = ''
+        self.msg = ''
         self.tags = []
         self.changes = {}
         self.cc_list = []