readme: mention how to run in-place
The README describes how to install Mercurial but it does not describe how to
run it in place (for developers). This adds a short paragraph to the README
describing how to do run Mercurial inplace.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.