update readme with dns-brute additional options

README.md

@@ -22,3 +22,14 @@ Take a screenshot of discovered HTTP(S) services using PhantomJS. Requires at le
 
 Evaluate the security of the response headers received from a request to the web server root folder. Requires at least Nmap version 7.0.
 
+
+### dns-brute2
+
+A fork of the `dns-brute` script included with nmap which attempts to enumerate hostnames by brute force guessing common subdomains. This version allows a list of resolvers to be provided so that each thread can query a separate DNS server and avoid potential rate limits.
+
+All additional options:
+
+- `dns-brute.maxhosts`: Limit the number of hosts to try. Default list is sorted by frequency so common names are tried first.
+- `dns-brute.resolverlist`: The filename of a list of dns resolvers to try.
+- `dns-brute.checkresolvers`: Perform a check to ensure each resolver is working before using it (takes more time)
+- `dns-brute.maxresolvers`: Limit the number of resolvers to use from the provided list. Number of supplied hosts times the number of threads is the most efficient value.