user-manual: fix inconsistent use of pull and merge
user-manual: fix inconsistent use of pull and merge

I used "git pull ." instead of "git merge" here without any explanation.
Stick instead to "git merge" for now (the equivalent pull syntax is
still covered in a later chapter).

Cc: Ramsay Jones <3e74413778ce9c8bebbbaedfd56741f6850faeaf@ramsay1.demon.co.uk>
Signed-off-by: "J. Bruce Fields" <51738506c1b2ccb0761f23bdc612c93babf738ea@citi.umich.edu>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git