Added cat

Had some issues with attributes and body, but I think the use of headers clears it up

apiary.apib

@@ -689,10 +689,30 @@ Import a tar file into ipfs
 
 + Response 200 (text/plain)
 
-## cat [GET /tar/cat]
-Export a tar file from ipfs
+## cat [GET /cat]
+Retrieves the object named by <ipfs-or-ipns-path> and outputs the data it contains.
 
-+ Response 200 (text/plain)
++ Parameters
+    + arg (string, required) - The path to the IPFS object(s) to be outputted
+
++ Response 200
+
+    + Headers
+        - Transfer-Encoding: chunked
+        - X-Stream-Output: 1
+
+    + Body
+
+    ```
+    $ curl -i http://localhost:5001/api/v0/cat?arg=QmeomffUNfmQy76CQGy9NdmqEnnHU9soCexBnGU3ezPHVH
+
+    HTTP/1.1 200 OK
+    Content-Length: 5
+    Transfer-Encoding: chunked
+    X-Stream-Output: 1
+
+    test
+    ```
 
 # Group tour
 This is a tour that takes you through various IPFS concepts,