docs(replay): clarify fast renderer option docs #9256

Job	Run time
Ready-to-merge gate / Missing "ready-to-merge" label	3s
diff_check	0s
detect-changes	0s
Build ios ${{ matrix.build-type }} ${{ matrix.ios-use-frameworks }}	0s
Build android ${{ matrix.build-type }}	0s
Build web	0s
	3s

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