Update README.md

Author: Carl Chang

README.md

@@ -1,10 +1,11 @@
 ## check_snmp
 #### Python script that checks components status against Dell or HPE servers with snmpwalk command
 
-Usage: `check_snmp.py [-h] [-r] host`
+Usage: `check_snmp.py [-h] [-v VERSION] [-c COMMUNITY] [-r] host`
 
 For example `check_snmp.py -r 192.168.1.120`
 
+By default SNMPv2c and community string public will be used. Different values can be specified with `-v` and `-c` respectively.
 The script will decide the manufacturer based on the OID returned on a initial call to snmpgetnext.
 
 The mibs folder contains lots of MIB files downloaded from Dell and HPE websites, also the ones downloaded by `snmp-mibs-downloader`.