Add faq entry about re-use of environments

Author: jugmac00

docs/changelog/2788.doc.rst

@@ -0,0 +1 @@
+Add faq entry about re-use of environments - by :user:`jugmac00`.

docs/faq.rst

@@ -121,6 +121,13 @@ tox 4 -- output changes
 - We now use colors for reporting, to help make the output easier to read for humans. This can be disabled via the
   ``TERM=dumb`` or ``NO_COLOR=1`` environment variables, or the ``--colored no`` CLI argument.
 
+tox 4 -- re-use of environments
++++++++++++++++++++++++++++++++
+
+- It is no longer possible to re-use environments. While this was possible with tox version 3, this behavior was never
+  supported and only worked by chance. You could possibly create a plugin to re-establish this functionality.
+
+
 New features in tox 4
 ---------------------
 Here is a non-exhaustive list of these.