Minor updates to the char device part of README

1) Add use of term 'Command ID'
2) Add use of term 'Command Return Value'
3) Add a missing ')'

Author: Kelvin Cao

README.rst

@@ -23,7 +23,7 @@ The primary means of communicating with the Switchtec management firmware is
 through the Memory-mapped Remote Procedure Call (MRPC) interface.
 Commands are submitted to the interface with a 4-byte command
 identifier and up to 1KB of command specific data. The firmware will
-respond with a 4 bytes return code and up to 1KB of command specific
+respond with a 4-byte return code and up to 1KB of command specific
 data. The interface only processes a single command at a time.
 
 
@@ -36,18 +36,18 @@ device: /dev/switchtec#, one for each management endpoint in the system.
 The char device has the following semantics:
 
 * A write must consist of at least 4 bytes and no more than 1028 bytes.
-  The first four bytes will be interpreted as the command to run and
-  the remainder will be used as the input data. A write will send the
+  The first 4 bytes will be interpreted as the Command ID and the
+  remainder will be used as the input data. A write will send the
   command to the firmware to begin processing.
 
 * Each write must be followed by exactly one read. Any double write will
   produce an error and any read that doesn't follow a write will
   produce an error.
 
 * A read will block until the firmware completes the command and return
-  the four bytes of status plus up to 1024 bytes of output data. (The
-  length will be specified by the size parameter of the read call --
-  reading less than 4 bytes will produce an error.
+  the 4-byte Command Return Value plus up to 1024 bytes of output
+  data. (The length will be specified by the size parameter of the read
+  call -- reading less than 4 bytes will produce an error.)
 
 * The poll call will also be supported for userspace applications that
   need to do other things while waiting for the command to complete.