[Wiki] Improved install instructions

[alexfu]

Hello, I made some improvements to the install documentation in the wiki that I would like to share.

Since GitHub has no built in way to make wiki pull requests, I've attached a patch file you can download and apply to the wiki...

keymaster.wiki-c40289e-improve-install-documentation.patch

git clone https://github.com/FutureTense/keymaster.wiki.git
cat keymaster.wiki-c40289e-improve-install-documentation.patch | git am

You can also view the updated wiki in my fork: https://github.com/alexfu/keymaster/wiki/Install-the-integration.