Documentation for "What is Rivet good for?"

Rivet is not for everyone, or for every project. Outlining the pros/cons seems like a good next step.

The issue names no documentation file or entry point. First locate the project's existing documentation, then determine where a “What is Rivet good for?” page belongs and gather the project context needed for balanced pros and cons; done means the guidance clearly explains when Rivet is and is not a good fit.

Written by the indexing model from the issue text.