docs: Create a glossary of common terms

[leohhhn]

Description

We should have a glossary file that will live in the docs, to shortly explain common terms (or link to other resources) that might not necessarily need a full page, or don't fit elsewhere. Examples could include:

• ABCI
• Account & sequence number
• Gas wanted & gas fee
• Render()
• std
• etc.

cc @wyhaines @michelleellen

[wyhaines]

I have started working on this, based on input from @thehowl at the end of last week. I'm working on it concurrently with drafts for a few of the basic onboarding tutorials that we need. I'll link the PR to this issue once I have the PR ready.