add a few more docs to existing funcs

Change-Id: I27317a59aba67c05ca1fd333e8f064c0edccb209
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/343185
Reviewed-by: LaMont Jones <lamontjones@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

git_command.py

@@ -158,6 +158,8 @@ def git_require(min_version, fail=False, msg=''):
 
 
 class GitCommand(object):
+  """Wrapper around a single git invocation."""
+
   def __init__(self,
                project,
                cmdv,

project.py

@@ -2671,6 +2671,7 @@ class Project(object):
       remote.Save()
 
   def _InitMRef(self):
+    """Initialize the pseudo m/<manifest branch> ref."""
     if self.manifest.branch:
       if self.use_git_worktrees:
         # Set up the m/ space to point to the worktree-specific ref space.
@@ -2700,6 +2701,16 @@ class Project(object):
     self._InitAnyMRef(HEAD, self.bare_git)
 
   def _InitAnyMRef(self, ref, active_git, detach=False):
+    """Initialize |ref| in |active_git| to the value in the manifest.
+
+    This points |ref| to the <project> setting in the manifest.
+
+    Args:
+      ref: The branch to update.
+      active_git: The git repository to make updates in.
+      detach: Whether to update target of symbolic refs, or overwrite the ref
+        directly (and thus make it non-symbolic).
+    """
     cur = self.bare_ref.symref(ref)
 
     if self.revisionId: