commit-patch: fix very important unterminate parenthesis in documentation that's been there since 2008

Two issues caused detection of buffers from patch filenames to fail:
  1. git uses a/some/file where cvs used some/file.
  2. (find-buffer-visiting) doesn't seem to work with relative paths.

Closes #14

README.md: Add Installation and Development sections, removing IPC::Run from Prerequisites since we're fatpacked now

Prior to this patch you could have a scenario where

- The filename in the first hunk refers to a real file
- The emacs buffer returned by (buffer-file-name) is a symlink to this file

Since (autodetect-patch-directory-root) comparse paths, this would make the
comparison fail in the wrong place, and (autodetect-patch-directory-root) would
return a wrong result

Normally the exe goes in /usr/bin and the .el files go in
/usr/share/site-lisp (or the /usr/local versions of those if you aren't
installing a package).

Fixes #11.

log-edit buffer is now called "*amend*" when amending and "*commit*" otherwise

This only works in Git, but then amending really only works in git.

According to https://en.wikipedia.org/wiki/All_rights_reserved