To see the docs for the gems you have installed (esp. gems in a
gemset), start the server using
gem server and then go to
git diff -M - the -M flag tells git to detect file moves - so you
can see what you changed in addition to renaming a file.
git diff -b - ignore changes that are only changes in white space.
git add -u puts changes in files it already knows about into the
index but does not add untracked files.
git commit -a is similar in
that it does not commit untracked files but commits changes
(modifications or file removals) to files it already knew about.