diff --git a/README.md b/README.md
index 1a7f8a1..74e4b10 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,7 @@ The following command line switches and their environment variable equivalents a
 |-d, --dnsPort		|DNS_PORT			 |Port the DNS proxy will bind to|
 |-h, --httpPort     |HTTP_PORT			 |Port the HTTP proxy will bind to|
 |-l, --logLevel		|LOG_LEVEL			 |Log level (defaults to "info") set to "null" to disable logging. To see a log of all network traffic set logLevel to "verbose"|
+|-p, --parentDataDirectory|PARENT_DATA_DIRECTORY      |Parent directory that will contain the data directories for the instances|
 
 For example: `tor-router -j 3 -s 9050` would start the proxy with 3 tor instances and listen for SOCKS connections on 9050.