Cleanup request MTU explanation.

Author: pauldemarco

README.md

@@ -105,7 +105,7 @@ characteristic.value.listen((value) {
 final mtu = await device.mtu.first;
 await device.requestMtu(512);
 ```
-Note that iOS will not allow that you request the MTU size, but will always try to negotiate the highest possible MTU (iOS supports up to MTU size 185)
+Note that iOS will not allow requests of MTU size, and will always try to negotiate the highest possible MTU (iOS supports up to MTU size 185)
 
 ## Reference
 ### FlutterBlue API