v1.0 post-MVP review

[samsmithnz]

Open Bugs:

• [x] some rounding errors. Need to round to 2 decimal places
• [x] Fix parameter names to be consistent - using the - separator

Enhancements:

• [x] Update docs, to include goals of this action, limitations, and full docs
• [x] Add output sample to docs

Feature requests:

• [x] Add error handling, especially to handle private repos, and workflows that don't exist (e.g. no results found)
• [x] Add user/PAT token to read from private repos
• [x] Add GitHub App auth
• [x] Handle multiple workflows (e.g. build+release, or Build+Dev+QA+Prod)
• [x] #24
• [x] #25
• [x] #37
• [x] #38