Document 'repo status' output

Signed-off-by: Shawn O. Pearce <sop@google.com>

subcmds/status.py

@@ -20,6 +20,44 @@ class Status(PagedCommand):
   helpSummary = "Show the working tree status"
   helpUsage = """
 %prog [<project>...]
+"""
+  helpDescription = """
+'%prog' compares the working tree to the staging area (aka index),
+and the most recent commit on this branch (HEAD), in each project
+specified.  A summary is displayed, one line per file where there
+is a difference between these three states.
+
+Status Display
+--------------
+
+The status display is organized into three columns of information,
+for example if the file 'subcmds/status.py' is modified in the
+project 'repo' on branch 'devwork':
+
+  project repo/                                   branch devwork
+   -m     subcmds/status.py
+
+The first column explains how the staging area (index) differs from
+the last commit (HEAD).  Its values are always displayed in upper
+case and have the following meanings:
+
+ -:  no difference
+ A:  added         (not in HEAD,     in index                     )
+ M:  modified      (    in HEAD,     in index, different content  )
+ D:  deleted       (    in HEAD, not in index                     )
+ R:  renamed       (not in HEAD,     in index, path changed       )
+ C:  copied        (not in HEAD,     in index, copied from another)
+ T:  mode changed  (    in HEAD,     in index, same content       )
+ U:  unmerged; conflict resolution required
+
+The second column explains how the working directory differs from
+the index.  Its values are always displayed in lower case and have
+the following meanings:
+
+ -:  new / unknown (not in index,     in work tree                )
+ m:  modified      (    in index,     in work tree, modified      )
+ d:  deleted       (    in index, not in work tree                )
+
 """
 
   def Execute(self, opt, args):