Fix introduction links to examples (#3266)
Fix introduction links to examples (#3266)

Existing links (to Github) were 404ing, so I changed them to point to slatejs.org.
Removed the final list item linking to the rest of the examples, since I can't see a page on slatejs.org that does that. Instead, I added a line after the examples list that talks about "View Source" and links to the Github folder listing.
ianstormtaylor/slate,ianstormtaylor/slate