docs: link rust cache issue

[risu729]

Summary

• add 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

[greptile-apps]

Greptile Summary

This PR adds a brief "Rust Cache" section to the README pointing readers to the known cache interaction issue (#215) that arises because mise installs Rust via rustup, rather than embedding a workaround directly in the docs.

• Adds a short paragraph under the caching section that links to issue cache breaks rustfmt install #215 for context and tracking.
• Keeps the README lean by deferring workaround details to the issue thread.

Confidence Score: 5/5

Pure documentation addition with no code changes; straightforward and safe to merge.

Only README.md is touched — a single new section that adds a link. Nothing functional is modified, and the linked issue exists in the same repository.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Adds a "Rust Cache" section linking to issue #215 about the known rustup cache interaction, replacing inline workaround documentation.

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

[gemini-code-assist]

Code Review

This pull request updates the README.md to include a section regarding Rust caching limitations when using rustup with mise. The feedback suggests clarifying the description of the issue and providing more immediate context about why the cache is affected, rather than relying solely on an external link.

[gemini-code-assist]

The term "cache interaction" is ambiguous and doesn't clearly convey that caching is partially ineffective for Rust. Using "caching limitation" or "issue" is more descriptive. Additionally, briefly explaining that the cause is the storage location helps users understand the problem immediately without needing to click the link for basic context.

Suggested change

	Rust has a known cache interaction because mise installs Rust through `rustup`.
	Rust has a known caching limitation because mise installs Rust through `rustup`, which stores data outside the default cache directory.

[risu729]

CI note: the remaining failures are the existing setup/provenance issue before this README-only change is exercised:

aube@1.9.1 has no provenance verification on linux-x64, but aube@1.6.2 had github-attestations

Local checks for this branch passed with mise run lint and git diff --check.

[github-actions]

This PR has been inactive for at least 7 days and currently has failing checks. Feel free to reopen or create a new PR if you'd like to continue working on this.