fix(docs): Fix NU6-related documentation #2071

Job	Run time
Check Cargo.lock is up to date	57s
Check deny.toml bans	31s
Install zebrad from lockfile without cache on ubuntu-latest	8m 47s
Check deny.toml bans --features default-release-binaries	33s
Check deny.toml bans --all-features	32s
Test stable on ubuntu-latest	31m 11s
Check for unused dependencies	16s
Check deny.toml sources	31s
Test beta on ubuntu-latest	31m 21s
Check deny.toml sources --features default-release-binaries	33s
Test stable on macos-latest	38m 18s
Check deny.toml sources --all-features	36s
Test stable on windows-latest	1h 0m 31s
Test beta on windows-latest	59m 26s
Open or update issues for OS integration failures	0s
	3h 54m 3s

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