docs: document --enable_entitlement_license option for Widevine #600

Job	Run time
Lint / Lint	14s
Settings / settings	3s
Official Docker image / Build	11m 53s
Test Linux distros / Matrix configuration	5s
Build and test / Matrix configuration	4s
Build docs / Build docs	56s
Build and test / linux x64 Debug static	9m 33s
Build and test / linux x64 Debug shared	9m 32s
Build and test / linux x64 Release static	15m 28s
Build and test / linux x64 Release shared	11m 11s
Build and test / osx x64 Debug static	24m 20s
Build and test / osx x64 Debug shared	24m 41s
Build and test / osx x64 Release static	11m 13s
Build and test / osx x64 Release shared	13m 6s
Build and test / osx arm64 Debug static	16m 59s
Build and test / osx arm64 Debug shared	16m 37s
Build and test / osx arm64 Release static	7m 18s
Build and test / osx arm64 Release shared	7m 17s
Build and test / win x64 Debug static	18m 33s
Build and test / win x64 Debug shared	15m 30s
Build and test / win x64 Release static	18m 47s
Build and test / win x64 Release shared	18m 40s
Build and test / linux arm64 Debug static	12m 16s
Build and test / linux arm64 Debug shared	34m 16s
Build and test / linux arm64 Release static	12m 38s
Build and test / linux arm64 Release shared	10m 47s
Test Linux distros / Alpine	12m 9s
Test Linux distros / ArchLinux	12m 39s
Test Linux distros / CentOS	11m 8s
Test Linux distros / Debian	11m 18s
Test Linux distros / Fedora	10m 33s
Test Linux distros / OpenSUSE	10m 43s
Test Linux distros / Ubuntu	9m 30s
	6h 39m 57s

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