RISCV: notice code wasn't showing

See merge request docs/docs.beagleboard.io!164

add RISC-V intro

See merge request docs/docs.beagleboard.io!163

Update basics

See merge request docs/docs.beagleboard.io!159

reference: https://pygments.org/docs/lexers/#module-pygments.lexers.diff

Site editing guide, link button, remove slug, forward latest to root, and custom 404.html template

See merge request docs/docs.beagleboard.io!157

this template page is not required now