docs: Glossary and Groups guide

[0xorbus]

• Revise glossary entries.
• Add glossary entry.
• Add Groups guide content.

[0xorbus]

@cedoor:

• I can't add you as a reviewer in this new repo.
• Do you think glossary should go under /technical-reference or stay where it is?
• I think glossary entries should reflect their use in Semaphore to provide additional value. For example, Merkle trees - if we can provide specific context in Semaphore or zk proofs/protocols then that adds value in addition to the Wikipedia entry.
• I need to work on a style guide a bit later, but glossary entry intros can be as short and to-the-point as possible--a rare case where a complete sentence isn't necessary.

[cedoor]

@0xorbus

• I just invited you in a Github docs team, you should more permissions
• I feel like it should be more visible. What do you think?
• I agree! It makes a lot of sense
• 👍🏽

[0xorbus]

@cedoor Resolved conflicts.