Elaborate why Tox recommends all the Pythons

https://bugzilla.redhat.com/show_bug.cgi?id=1645025

python-tox.spec

@@ -37,6 +37,13 @@ BuildRequires:  python3-setuptools
 BuildRequires:  python3-setuptools_scm
 
 # Recommend "all the Pythons"
+# Why? Tox exists to enable developers to test libraries against various Python
+# versions, with just "dnf install tox" and a config file.
+# See: https://developer.fedoraproject.org/tech/languages/python/python-installation.html#using-virtualenv
+# Tox itself runs on the system python3 (i.e. %%{python3_version},
+# however it launches other Python versions as subprocesses.
+# It recommends all Python versions it supports. (This is an exception to
+# the rule that Fedora packages may not require the alternative interpreters.)
 Recommends:     python27
 Recommends:     python34
 Recommends:     python35