user-manual: point to README for gitweb information
user-manual: point to README for gitweb information

I'd like complete gitweb setup instructions some day, but for now just
refer to the gitweb README.

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