sg: introduce `sg wut` for looking up Sourcegraph acronyms and lingo

Created by: courier-new

Inspired by the wonderful @slimsag's original document WDYMWDIM, from which the dictionary definitions here are directly taken, and @muratsu's suggestion to add this to sg. 😄 I think having a dictionary for business/engineering acronyms and Sourcegraph-specific lingo is a HUGE value add, particularly for new hires and early-career folks.

https://user-images.githubusercontent.com/8942601/152894270-a3cb7d12-dcf2-4826-9b20-d1de398429fe.mov

(My first "significant" contribution to sg here so appreciate any feedback, sorry I don't know the best person/people to tag for review!! 😅)