Update file README.md
I changed the word order of the sentence： "Define an RPC service in a .proto file called 'PropertyLookup'". Because in OH, I saw many students name the proto file as PropertyLookup.proto.
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I changed the word order of the sentence： "Define an RPC service in a .proto file called 'PropertyLookup'". Because in OH, I saw many students name the proto file as PropertyLookup.proto.