Close #19407: New installation & distribution guides

- based on pip and other PyPA tools
- includes references to the new Python Packaging User Guide
  where appropriate (and the relevant section is at least
  partially filled in)
- started new FAQ sections
- both guides aim to introduce users to basic open source
  concepts if they aren't aware of them
- existing guides have been relocated (now linked from the
  distutils docs) rather then removed, since there is
  some needed material that has yet to be relocated to the
  distutils docs as a reference for the legacy formats
diff --git a/Doc/tutorial/whatnow.rst b/Doc/tutorial/whatnow.rst
index 7fcbdc3f..979f587 100644
--- a/Doc/tutorial/whatnow.rst
+++ b/Doc/tutorial/whatnow.rst
@@ -21,8 +21,8 @@
   and many other tasks. Skimming through the Library Reference will give you an
   idea of what's available.
 
-* :ref:`install-index` explains how to install external modules written by other
-  Python users.
+* :ref:`installing-index` explains how to install additional modules written
+  by other Python users.
 
 * :ref:`reference-index`: A detailed explanation of Python's syntax and
   semantics.  It's heavy reading, but is useful as a complete guide to the