Summary:
`/docs/understand.html` doesn't exist anymore. Also "learn more" in the landing page pointed to `/docs/understand.html` which was broken. Pointed "Learn More" to getting started doc page.
`/docs/understand.html` explained about rsocket which will be little overwhelming for the user to be navigated to right from the landing page.
Also removed the links pointing to `/docs/understand.html`
Reviewed By: passy
Differential Revision: D15147954
fbshipit-source-id: cbd67d7f234c438507f24db946cd463e8827cb78
e7200e36a3