chore: warn in docs that precompiled langs aren't yet supported

[slevithan]

Per discussion separately, adding a warning discouraging the use of precompiled languages for now until #918 is resolved.

[netlify]

✅ Deploy Preview for shiki-matsu ready!

Name	Link
🔨 Latest commit	adc5878
🔍 Latest deploy log	https://app.netlify.com/sites/shiki-matsu/deploys/67b9ae086f38e3000809ebbd
😎 Deploy Preview	https://deploy-preview-944--shiki-matsu.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[netlify]

✅ Deploy Preview for shiki-next ready!

Name	Link
🔨 Latest commit	adc5878
🔍 Latest deploy log	https://app.netlify.com/sites/shiki-next/deploys/67b9ae089d62d0000809ae1a
😎 Deploy Preview	https://deploy-preview-944--shiki-next.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.11%. Comparing base (4720501) to head (adc5878).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #944   +/-   ##
=======================================
  Coverage   95.11%   95.11%           
=======================================
  Files          89       89           
  Lines        7366     7366           
  Branches     1528     1529    +1     
=======================================
  Hits         7006     7006           
  Misses        352      352           
  Partials        8        8           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.