docs(cloudflare): add info regarding runtimeConfig and environment variables

[manniL]

🔗 Linked issue

Related: #272

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Give some info regarding CF env variables.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #958 (8835d2c) into main (5da951b) will increase coverage by 1.09%.
The diff coverage is n/a.

❗ Current head 8835d2c differs from pull request most recent head e2aeb4d. Consider uploading reports for the commit e2aeb4d to get more accurate results

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
+ Coverage   66.50%   67.59%   +1.09%     
==========================================
  Files          57       59       +2     
  Lines        4221     6030    +1809     
  Branches      450      679     +229     
==========================================
+ Hits         2807     4076    +1269     
- Misses       1410     1945     +535     
- Partials        4        9       +5     

Impacted Files	Coverage Δ
src/rollup/plugins/dynamic-require.ts	26.56% <0.00%> (-33.80%)	⬇️
src/storage.ts	17.50% <0.00%> (-30.99%)	⬇️
src/rollup/plugins/esbuild.ts	53.33% <0.00%> (-13.84%)	⬇️
src/presets/firebase.ts	18.01% <0.00%> (-12.51%)	⬇️
src/presets/azure.ts	8.57% <0.00%> (-7.67%)	⬇️
src/compress.ts	90.55% <0.00%> (-4.84%)	⬇️
src/presets/azure-functions.ts	21.62% <0.00%> (-4.41%)	⬇️
src/utils/tree.ts	12.12% <0.00%> (-3.88%)	⬇️
src/rollup/plugins/virtual.ts	97.14% <0.00%> (-2.86%)	⬇️
src/rollup/config.ts	88.30% <0.00%> (-2.78%)	⬇️
... and 33 more

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