chore: ORM-1106 document mysql non support multi schema #4676

Job	Run time
compilation-push	-1s
compilation (ubuntu-latest, schema-engine-cli) / compile schema-engine-cli @ ubuntu-latest	5m 16s
compilation (windows-latest, query-engine) / compile query-engine @ windows-latest	9m 57s
compilation (ubuntu-latest, prisma-fmt) / compile prisma-fmt @ ubuntu-latest	1m 49s
compilation (windows-latest, query-engine-node-api) / compile query-engine-node-api @ windows-latest	10m 49s
compilation (ubuntu-latest, query-engine-node-api) / compile query-engine-node-api @ ubuntu-latest	5m 29s
compilation (windows-latest, prisma-fmt) / compile prisma-fmt @ windows-latest	4m 45s
compilation (ubuntu-latest, query-engine) / compile query-engine @ ubuntu-latest	5m 31s
compilation (windows-latest, schema-engine-cli) / compile schema-engine-cli @ windows-latest	9m 51s
	53m 26s

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