Enable help for serial readString() (#609)

docs/reference/serial/read-string.md

@@ -1,6 +1,6 @@
 # Serial Read String
 
-Read the buffered serial data as a string
+Read the buffered serial data as a string.
 
 ```sig
 serial.readString();
@@ -8,7 +8,7 @@ serial.readString();
 
 ## Returns
 
-* a [string](/types/string) containing input from the serial port. Empty if no data available.
+* a [string](/types/string) containing input from the serial port. The string is empty if no data is available.
 
 ## Example