Write a man page

[ffes]

git open --help tries to open the man page for the command but there is no man page.

Hopefully somebody is brave enough to write one!

Not sure if the source of such a man page should be troff or something better like restructuredtext or markdown (which can be converted to man pages with rst2man or md2man, but require additional build dependencies)

A large part of the documentation could come from the README.md

[ffes]

I've mostly copy/pasted a man page from the README.md and added some own texts (know that I am not a native English speaker). From that markdown I have generated a man page.

Since the project uses Node, I used marked-man to generate git-open.1. I attached them both in a zip here, for people to see.

Please let know what you think. I gladly make a PR for this, but first the texts in #93 and #99 need to get merged so those can be reused as well.

I think that when we have a man page (in markdown) most of the documentation in README.md should be replaced with a link to the markdown source of the man page.

git-open-1.zip
To view git-open.1 use man ./git-open.1