Stash startup pages "install git" and "upgrade git" have no links or instructions

The page just says Stash can't run and the user needs to install or upgrade git.

When they do, git may now be in the PATH, but only for new shell/command terminals.

The page should link to the correct git download where is says "install/upgrade git" and should have a page of instructions on how to do this (including how to restart Stash).

Talk to pwatson about how we might structure our install docs so we can link to a page that has unix and windows install instructions.

Make the johnson link to this page.