nmbug: Document early 'nmbug checkout'

And explain the side-effects from mussing local messages.  Based on
discussion with DKG in #notmuch on freenode today.

Reported-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/nmbug.mdwn b/nmbug.mdwn
index 44a1a20..e962c06 100644
--- a/nmbug.mdwn
+++ b/nmbug.mdwn
@@ -10,6 +10,12 @@ There is a dump of (some views of) the nmbug [[status|http://nmbug.notmuchmail.o
 0. Make sure that the whole [notmuch@notmuchmail.org mailing list
    archive][archive] is available in your email database.
 
+   If you are missing messages which are tagged in the nmbug
+   repository, `nmbug status` will complain with U-prefixed lines and
+   you will have to jump through some hoops to create commits that
+   alter tags for those messages.  Most other nmbug operation will be
+   unaffected.
+
 1. Install and use nmbug from notmuch version **0.19** or newer, and
    either Python 2.7 or anything from the 3.x line.
 
@@ -21,6 +27,13 @@ There is a dump of (some views of) the nmbug [[status|http://nmbug.notmuchmail.o
 
    `$ nmbug clone http://nmbug.notmuchmail.org/git/nmbug-tags.git`
 
+4. Clobber your local `notmuch::…` tag namespace with:
+
+   `$ nmbug checkout`
+
+   Without this, `nmbug status` will list all of the upstream tags as
+   deleted (with the D prefix).
+
 ## Using nmbug, simple example
 
     # get the latest version of the tags