Update and slightly clarify instructions in build_detect_platform (#1301)
Update and slightly clarify instructions in build_detect_platform (#1301)


tsheasha/rocksdb,facebook/rocksdb,Andymic/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,norton/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,bbiao/rocksdb,facebook/rocksdb,vmx/rocksdb,wenduo/rocksdb,norton/rocksdb,facebook/rocksdb,wenduo/rocksdb,vmx/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,facebook/rocksdb,Andymic/rocksdb,norton/rocksdb,facebook/rocksdb,vmx/rocksdb,Andymic/rocksdb,norton/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,tsheasha/rocksdb,norton/rocksdb,wat-ze-hex/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,bbiao/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,norton/rocksdb,OverlordQ/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,wenduo/rocksdb,vmx/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,vmx/rocksdb,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,norton/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,wenduo/rocksdb,SunguckLee/RocksDB,norton/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,bbiao/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,tsheasha/rocksdb