doc/update-readme

[lili2311]

• [ ] Tests written and linted ℹ︎
• [x] Documentation written in Wiki/README
• [ ] Commit history is tidy & follows Contributing guidelines ℹ︎

What this does

Update docs to explain this repo is in critical bug fixes mode only. https://github.com/snyk-tech-services/snyk2spdx/issues/46

[CLAassistant]

All committers have signed the CLA.

[aarlaud]

:tada: This PR is included in version 1.7.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: