Mention wp site switch-language in readme

Author: swissspidy

README.md

@@ -766,6 +766,26 @@ wp language theme update [<theme>...] [--all] [--dry-run]
     Translation updated successfully.
     Success: Updated 1/1 translation.
 
+
+
+### wp site switch-language
+
+Activates a given language.
+
+~~~
+wp site switch-language <language>
+~~~
+
+**OPTIONS**
+
+	<language>
+		Language code to activate.
+
+**EXAMPLES**
+
+    $ wp site switch-language ja
+    Success: Language activated.
+
 ## Installing
 
 This package is included with WP-CLI itself, no additional installation necessary.

composer.json

@@ -53,7 +53,8 @@
             "language theme install",
             "language theme list",
             "language theme uninstall",
-            "language theme update"
+            "language theme update",
+            "site switch-language"
         ]
     },
     "autoload": {