docs: link rust cache issue

[risu729]

Summary

• recreate docs: link rust cache issue #483 by adding a short README link to the known Rust cache issue
• avoid documenting a workaround in the README

Test plan

• mise run lint
• git diff --check

[gemini-code-assist]

Code Review

This pull request updates the README.md file to document a known cache interaction issue with Rust when installed via rustup, referencing an external issue for context. There are no review comments to address.

[greptile-apps]

Greptile Summary

Adds a short "Rust Cache" section to the README documenting the known cache interaction when mise manages Rust via rustup, pointing readers to issue #215 rather than inline-documenting a workaround.

• Inserts a three-line section under the caching docs with a direct link to the upstream issue for further context.

Confidence Score: 5/5

Documentation-only change with no runtime impact — safe to merge.

The change is a three-line addition to the README that adds a heading and a link to an existing GitHub issue. There is no logic, configuration, or behaviour being altered.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Adds a "Rust Cache" section pointing readers to issue #215 for known cache interaction with rustup-managed Rust installations

_{Reviews (1): Last reviewed commit: "docs: link rust cache issue" | Re-trigger Greptile}