[feat.request] add comparative in README.md to error-prone alternatives

I think it would be interesting to add to the README.md a brief table comparative explaining how error-prone complement|competes|overlaps with similar solutions like SpotBugs, OpenRewrite, SonarQube, ... (many others I just ignore).

Start in README.md and review its existing structure and terminology. Research how Error Prone compares with SpotBugs, OpenRewrite, SonarQube, and similar solutions, then add a brief comparison table covering complementarity, competition, or overlap. Done means the README clearly presents these distinctions without changing unrelated documentation.

Written by the indexing model from the issue text.