Link to usage examples (#428)

* Link to usage doc

* Better link

---------

Co-authored-by: Kevin McCormack <kevin@mccormack.tech>

Author: sebbASF

README.rdoc

@@ -23,7 +23,7 @@ the most recent LDAP RFCs (4510–4519, plus portions of 4520–4532).
 
 == Synopsis
 
-See {Net::LDAP on rubydoc.info}[https://www.rubydoc.info/github/ruby-ldap/ruby-net-ldap] for documentation and usage samples.
+See {Net::LDAP on rubydoc.info}[https://www.rubydoc.info/github/ruby-ldap/ruby-net-ldap/Net/LDAP] for documentation and usage samples.
 
 == Requirements