Added documentation.

README.md

@@ -75,11 +75,12 @@ The segments that are currently available are:
 * [dir](#dir) - Your current working directory.
 * **history** - The command number for the current line.
 * [ip](#ip) - Shows the current IP address.
-* **load** - Your machines 5 minute load average and free RAM.
+* **load** - Your machines 5 minute load average.
 * **node_version** - Show the version number of the installed Node.js.
 * **nvm** - Show the version of Node that is currently active, if it differs from the version used by NVM
 * **os_icon** - Display a nice little icon, depending on your operating system.
 * **php_version** - Show the current PHP version.
+* [ram](#ram) - Show free RAM and used Swap.
 * [rbenv](#rbenv) - Ruby environment information (if one is active).
 * [rspec_stats](#rspec_stats) - Show a ratio of test classes vs code classes for RSpec.
 * [status](#status) - The return code of the previous command, and status of background jobs.
@@ -154,6 +155,15 @@ following variable in your `~/.zshrc`.
 
     POWERLEVEL9K_STATUS_VERBOSE=false
 
+##### ram
+
+By default this segment shows you free RAM and used Swap. If you want to show
+only one value, you can specify `POWERLEVEL9K_RAM_ELEMENTS` and set it to either
+`ram_free` or `swap_used`. Full example:
+
+    # Show only used swap:
+    POWERLEVEL9K_RAM_ELEMENTS=(swap_used)
+
 ##### symphony2_tests
 
 See [Unit Test Ratios](#unit-test-ratios), below.