Update docs

Author: Egor Panfilov

INSTALL

@@ -14,6 +14,10 @@ You also need xmlsec, which you can find here:
 
     http://www.aleksey.com/xmlsec/
 
+On Ubuntu:
+
+    sudo apt install xmlsec1
+
 You may also need:
 
  mako

docs/howto/config.rst

@@ -639,7 +639,7 @@ Where the endpoints for the services provided are.
 This directive has as value a dictionary with one or more of the following keys:
 
 * artifact_resolution_service (aa, idp and sp)
-* assertion_consumer_service (sp)
+* `assertion_consumer_service <https://wiki.shibboleth.net/confluence/display/CONCEPT/AssertionConsumerService>`_ (sp) 
 * assertion_id_request_service (aa, idp)
 * attribute_service (aa)
 * manage_name_id_service (aa, idp)