WIP adding links to issues

Addresses pypa#8210 , pypa#8253

docs/html/user_guide.rst

@@ -1082,9 +1082,9 @@ install x y`` in a single command.
 
 We are also changing our support for :ref:`Constraints Files`:
 
-* Unnamed requirements are not allowed as constraints (see `#6628`_)
-* Links are not allowed as constraints
-* Constraints cannot have extras
+* Unnamed requirements are not allowed as constraints (see `#6628`_ and `#8210`_)
+* Links are not allowed as constraints (see `#8253`_)
+* Constraints cannot have extras (see `#6628`_)
 
 
 How to test
@@ -1226,3 +1226,5 @@ As discussed in `our announcement on the PSF blog`_, the pip team are in the pro
 .. _our announcement on the PSF blog: http://pyfound.blogspot.com/2020/03/new-pip-resolver-to-roll-out-this-year.html
 .. _tensorflow: https://pypi.org/project/tensorflow/
 .. _#6628: https://github.com/pypa/pip/issues/6628
+.. _#8210: https://github.com/pypa/pip/issues/8210
+.. _#8253: https://github.com/pypa/pip/issues/8253