commands: document the "common" class attribute

Switch it to uppercase to make it clear it's a constant, and add
documentation so its usage is clear.

Change-Id: I6d281a66a90b5908b3131585c9945e88cfe815ea
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/309322
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/subcmds/checkout.py b/subcmds/checkout.py
index 4d8009b1..9b429489 100644
--- a/subcmds/checkout.py
+++ b/subcmds/checkout.py
@@ -20,7 +20,7 @@ from progress import Progress
 
 
 class Checkout(Command):
-  common = True
+  COMMON = True
   helpSummary = "Checkout a branch for development"
   helpUsage = """
 %prog <branchname> [<project>...]