Add docs for isDlcInstalled

docs/apps.rst

@@ -6,6 +6,7 @@ List of Functions
 -----------------
 
 * :func:`apps.getCurrentGameLanguage`
+* :func:`apps.isDlcInstalled`
 
 
 Function Reference
@@ -25,3 +26,18 @@ Function Reference
 
     print("The games current language is " .. Steam.apps.getCurrentGameLanguage())
 
+
+.. function:: apps.isDlcInstalled(appID)
+
+    :param number appID: The App ID of the DLC to check.
+    :returns: (`boolean`) true if the user owns the DLC and it's currently installed, otherwise false.
+    :SteamWorks: `GetCurrentGameLanguage <https://partner.steamgames.com/doc/api/ISteamApps#BIsDlcInstalled>`_
+
+	Checks if the user owns a specific DLC and if the DLC is installed.
+
+
+**Example**::
+
+    if Steam.apps.isDlcInstalled(12345) then
+        -- Unlock game content
+    end