Exclude docs/ from the Composer dist archive #81

Problem

The README alignment (#79) moved reference material into docs/configuration.md and docs/rule-set.md. .gitattributes has no export-ignore entry for /docs, so both pages now ship inside every composer require pekral/rector-rules download.

git archive HEAD already includes AGENTS.md, .agents/ and .codex/ as well, for the same reason.

Proposal

Decide whether consumers should get these files. If not, add to .gitattributes:

/docs export-ignore

and consider the same for AGENTS.md, .agents/ and .codex/.