Added documentation for the ip segment.

README.md

@@ -41,6 +41,7 @@ this theme focus on four primary goals:
   - [The AWS Profile Segment](#the-aws-profile-segment)
   - [The 'context' Segment](#the-context-segment)
   - [The 'dir' segment](#the-dir-segment)
+  - [The 'ip' segment](#the-ip-segment)
   - [The 'time' segment](#the-time-segment)
   - [Unit Test Ratios](#unit-test-ratios)
   - [The 'vcs' Segment](#the-vcs-segment)
@@ -293,6 +294,15 @@ In each case you have to specify the length you want to shorten the directory
 to. So in some cases `POWERLEVEL9K_SHORTEN_DIR_LENGTH` means characters, in 
 others whole directories.
 
+#### The 'ip' segment
+
+This segment shows you your current internal IP address. It tries to examine
+all currently used network interfaces and prints the first address it finds.
+In the case that this is not the right IP address you can specify the correct
+network interface by setting:
+
+    POWERLEVEL9K_IP_INTERFACE="eth0"
+
 #### The 'time' segment
 
 By default the time is show in 'H:M:S' format. If you want to change it,