Small Spelling Corrections and Insertion of links

[Fbalashov]

Hi André I stumbled upon your repo in my search for a definitive guide on building lint rules for android. I just started going through it and I appreciate the organization of information, examples and detail you used to make the guide.

While reading I noticed a few typos and areas where I would have appreciated links. In the spirit of your contribution readme I wanted to check you'd like a PR for these corrections and additions? I plan to put the typo corrections in one commit and the addition of links in another.

[Fbalashov]

I created a PR with my first pass of changes here