rdk: Add sshconfig info

 Some users (e.g., vendors) likely don't use the same
 username as their comcast ntid. Add some info for
 setting the ntid for ssh logins on this host.

Signed-off-by: Jesse Crews <jesse_crews@comcast.com>
Change-Id: I7a2923290cab4cffc163b8230d88345878606dc8
diff --git a/README.rdk.md b/README.rdk.md
index 43d39a4..433197c 100644
--- a/README.rdk.md
+++ b/README.rdk.md
@@ -9,6 +9,14 @@
 
 Make sure you load your [SSH public key(s)](https://rdkgerrithub.stb.r53.xcal.tv/settings/#SSHKeys).
 
+If your machine login isn't the same as your comcast ntid, add this to your
+~/.ssh/config:
+```
+Host rdkgerritprod.stb.r53.xcal.tv
+User <youruser>
+IdentityFile ~/.ssh/<yourkey> #optional, if you want to specify a specific private key
+```
+
 You can test your access with:
 ```
 ssh-keyscan -t rsa -p 29418 rdkgerrithub.stb.r53.xcal.tv >> ~/.ssh/known_hosts