Hyperlinked phoenix_eighties in Custom Color Scheme and Eighties mode for selected tab

Added an internal hyperlink to **Eighties mode for selected tab** for `phoenix_eighties` in the **Custom Color Scheme** section so that it's easier to navigate for the reader.
Fixed typo: `-you`, `+your` in Alternate Colors section
Merge pull request #20 from rishabhsrao/master

Slight improvement to the read me