emacs: Add README.

Initial draft of README. Includes short description, installation, and
basic usage.

BUG=None
TEST=Followed README with unconfigured init.el and invoked commands.

Change-Id: If9d4839b1bd49f6713dea5c5c6c5ef6e7593387d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2335037
Tested-by: Aaron Massey <aaronmassey@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Sean McAllister <smcallis@google.com>
Commit-Queue: Aaron Massey <aaronmassey@chromium.org>
4 files changed