Added documentation for ircNotification and writeCapabilities steps

vars/ircNotification.txt

@@ -0,0 +1,9 @@
+<p>Sends a notice to IRC with the current build result.</p>
+<dl>
+  <dt>ircNotification([server, nick, channel])</dt>
+  <dd>
+    Sends a notification to IRC with the specified <code>server</code>,
+    <code>nick</code>, and <code>channel</code>. By default it will connect to
+    <code>irc.mozilla.org:6697</code> as <code>fxtest</code> and join the
+    <code>#fx-test-alerts</code> channel.
+</dl>

vars/writeCapabilities.txt

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+<p>Write desired capabilities to a JSON file.</p>
+<dl>
+  <dt>writeCapabilities(capabilities, [path])</dt>
+  <dd>
+    Writes a JSON file containing the items from the <code>capabilities</code>
+    map to the specified <code>path</code> (for use by
+    <a href="http://pytest-selenium.readthedocs.io/en/latest/user_guide.html#capabilities-files">
+    pytest-selenium</a>). If omitted, the <code>path</code> defaults to
+    <code>capabilities.json</code> in the working directory.
+  </dd>
+</dl>