Update env var documentation in `rerun --help` #14550

Job	Run time
cpp-paths-filter	5s
docs-paths-filter	2s
python-paths-filter	4s
rust-paths-filter	3s
web-paths-filter	7s
Checks / Lint markdown	15s
Checks / Rerun lints	34s
Checks / Check if running codegen would produce any changes	1m 15s
Checks / markdown-paths-filter	5s
Checks / Spell Check	5s
Checks / Misc formatting	16s
Update PR Body / Update PR body	16s
Deploy Landing Preview	0s
Python Checks	0s
C++ tests	0s
Minimum CLI Build / Set Config (linux-x64)	3s
Rust Checks / Test on macOS and Windows	0s
Rust Checks / Rust lints (fmt, check, clippy, tests, doc)	8m 46s
Checks / Check links	0s
Build web viewer / Build web viewer	2m 45s
Build rerun_js / Build rerun_js	3m 3s
Minimum CLI Build / Build rerun-cli (ubuntu-latest-16-cores)	5m 13s
Upload Web / Upload web build to google cloud (wasm32 + wasm-bindgen)	9s
Save PR Summary / Create HTML summary for PR	45s
Minimum Wheel Build / Set Config (linux-x64)	1s
Minimum Wheel Build / Build Wheels (ubuntu-latest-16-cores)	2m 30s
Minimum Wheel Test / Set Config (linux-x64)	1s
Minimum Wheel Test / Test Wheels (ubuntu-latest-16-cores)	3m 10s
	29m 33s

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