add help blurb for "extralargefile" #134963

Job	Run time
Change detection / Compute changed files	10s
Check if Autoconf files are up to date	22s
Docs	0s
Check if generated files are up to date	4m 28s
Address sanitizer (ubuntu-24.04)	8m 42s
Ubuntu SSL tests with OpenSSL (ubuntu-24.04, 3.0.15)	2m 51s
Ubuntu SSL tests with OpenSSL (ubuntu-24.04, 3.1.7)	2m 53s
Hypothesis tests on Ubuntu	6m 35s
Windows MSI${{ '' }}	0s
Ubuntu SSL tests with OpenSSL (ubuntu-24.04, 3.2.3)	2m 54s
Ubuntu SSL tests with OpenSSL (ubuntu-24.04, 3.3.2)	2m 53s
Ubuntu SSL tests with OpenSSL (ubuntu-24.04, 3.4.0)	2m 39s
CIFuzz	0s
Thread sanitizer / Thread sanitizer	3m 3s
Thread sanitizer (free-threading) / Thread sanitizer	7m 35s
WASI / build and test	5m 6s
macOS (free-threading) / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	5m 38s
macOS / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	4m 29s
Ubuntu / build and test (ubuntu-24.04)	8m 24s
Ubuntu / build and test (ubuntu-24.04-aarch64)	7m 14s
macOS / build and test (macos-13)	11m 28s
Ubuntu (free-threading) / build and test (ubuntu-24.04)	11m 53s
Ubuntu (free-threading) / build and test (ubuntu-24.04-aarch64)	13m 10s
Windows / build and test (arm64)	3m 15s
Windows (free-threading) / build and test (arm64)	2m 41s
Windows / build and test (Win32)	16m 15s
Windows / build and test (x64)	17m 0s
Windows (free-threading) / build and test (x64)	22m 45s
All required checks pass	2s
	2h 54m 25s

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