Adds content for each of major navigation links.
Adds content for each of major navigation links.

No anchors yet, so navigation links don't jump to the position yet.

gaurav/phyloref.github.io,phyloref/phyloref.github.io,phyloref/phyloref.github.io,phyloref/phyloref.github.io,gaurav/phyloref.github.io,phyloref/phyloref.github.io,gaurav/phyloref.github.io,gaurav/phyloref.github.io