Docs: Document troubleshooting process for License Finder

Problem to solve

Pipeline for License Finder project is complex and when something fails, it requires knowledge to fix it. We need to document tips for troubleshooting in README to simplify this process.

Further details

Proposal

Add section troubleshooting to https://gitlab.com/gitlab-org/security-products/analyzers/license-finder/-/blob/main/README.md when place next information:

1. general information about pipeline stages and jobs and what that stages are needed for, what tools are used (omnibus, asdf etc)
2. information how to resolve issues with failing asdf plugins, as we ran into this issue a few times #298720 (comment 495337260)
3. any other findings

Who can address the issue

someone knowledgeable about License Finder project

Other links/references

This is a follow-up from #298720 (closed)