Document Chotto API key and URL setup

Added comments for Chotto configuration setup in the sample config file.

cfg/conf.sample.php

@@ -266,6 +266,17 @@ dir = PATH "data"
 ;version = "latest"
 ;bucket = "my-bucket"
 
+;[chhoto]
+; - Chotto requires you to make a post call with a generated API key.
+;   use this section to setup the API key and URL. In order to use this section,
+;   "urlshortener" needs to point to the base URL of your PrivateBin
+;   instance with "?shortenviachhoto&link=" appended. For example:
+;   urlshortener = "${basepath}?shortenviachhoto&link="
+;    This URL will in turn call Chhoto-url on the server side, using the URL from
+;   "apiurl" and the API Key from the "apikey" parameters below.
+; apiurl = "https://chhoto-url.example.com/api/new"
+; apikey = "your_api_key"
+    
 ;[shlink]
 ; - Shlink requires you to make a post call with a generated API key.
 ;   use this section to setup the API key and URL. In order to use this section,