PHPLIB-187: Remind users to encode connection URIs

docs/includes/apiargs-MongoDBClient-method-construct-param.yaml

@@ -7,6 +7,12 @@ description: |
   </reference/connection-string>` for formatting.
 
   Defaults to ``"mongodb://127.0.0.1:27017"`` if unspecified.
+
+  Any special characters in the URI components need to be encoded according to
+  `RFC 3986 <http://www.faqs.org/rfcs/rfc3986.html>`_. This is particularly
+  relevant to the username and password, which can often include special
+  characters such as ``@``, ``:``, or ``%``. The :php:`rawurlencode()
+  <rawurlencode>` function may be used to encode constituent parts of the URI.
 interface: phpmethod
 operation: ~
 optional: true