Spec for signing with local key

[iamsamirzon]

Summary
Alpha-1 implemented signing with local key. Remaining work on what file format to support and secure the key behind a password;
Intended Outcome
Notation CLI implementations allows for this use case
The specification PR is merged
Additional context
Today what we support is plain-text key; Need to do research on how this is done for open source projects;

[iamsamirzon]

This is related to line #12 in the spreadsheet.

[vaninrao10]

Remaining work for signing with local key (use case 2 & 4 in the table that Yi created [https://github.com//issues/15#issuecomment-1283421971]
has still one outstanding item to "password protect" the local signing keys. Otherwise the work for signing and verifying with local/on-disk keys is complete.

[iamsamirzon]

Based on the agreement in NV2 community call on 12/5/2022, moving this out of RC-2