fix link syntax (#219)

* fix link syntax, update link to point to a specific guide

Author: Chris Cho

source/fundamentals/connection.txt

@@ -1,3 +1,5 @@
+.. _java-connection-guide:
+
 ================
 Connection Guide
 ================

source/includes/connect-guide-note.rst

@@ -1,5 +1,5 @@
 .. note::
 
-    This example connects to an instance of MongoDB using a connection string.
+    This example connects to an instance of MongoDB using a connection URI.
     To learn more about connecting to your MongoDB instance, see the
-    `connection guide </fundamentals/connection>`_.
+    :ref:`connection guide <connect-to-mongodb>`.