Documentation: build redo-jch.sh from master..jch

Rebuilding the 'jch' branch begins by reintegrating any topics between
'master' and 'jch', not 'master' and 'seen'.

In the maintainer guide, the documentation isn't quite right, since the
initial input to Meta/Reintegrate is "master..seen", not "master..jch".
This can lead to confusing results when generating the Meta/redo-jch.sh
script for the first time.

Additionally, rebuilding 'jch' takes place in two steps. First, running
the script up to the first "### match next" cut-line, and then comparing
the result with what's on 'next' (i.e. with "git diff jch next"). Then,
the remaining set of topics get merged down to 'jch' (which aren't on
'next') by running the entire "redo-jch.sh" script.

Clarify the documentation to reflect this.

Signed-off-by: Taylor Blau <[email protected]>

Author: ttaylorr

Documentation/howto/maintain-git.txt

@@ -231,7 +231,7 @@ by doing the following:
  - Prepare 'jch' branch, which is used to represent somewhere
    between 'master' and 'seen' and often is slightly ahead of 'next'.
 
-     $ Meta/Reintegrate master..seen >Meta/redo-jch.sh
+     $ Meta/Reintegrate master..jch >Meta/redo-jch.sh
 
    The result is a script that lists topics to be merged in order to
    rebuild 'seen' as the input to Meta/Reintegrate script.  Remove
@@ -283,6 +283,11 @@ by doing the following:
 
      $ git diff jch next
 
+   Then build the rest of 'jch':
+
+     $ git checkout jch
+     $ sh Meta/redo-jch.sh
+
    When all is well, clean up the redo-jch.sh script with
 
      $ sh Meta/redo-jch.sh -u