Remove the "jgit is slow" remark from README
Historically this may have been true, back when we built things
on the lib.Commit and lib.Tree API. Those APIs are quickly being
rebuilt around RevWalk and TreeWalk, which are much more powerful
and significantly faster.
Most testing indicates that once the JIT has had a chance to do
its optimization magic on the jgit library we get performance that
really does rival C git running on the same system. Since C git
is so ridiculously fast we're probably still beating many of the
other VCS tools available.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>