Added intro to 'How to teach this'

Author: astrofrog

peps/pep-0771.rst

@@ -573,6 +573,26 @@ There are no known security implications for this PEP.
 How to teach this
 =================
 
+This section outlines information that should be made available to people in
+different groups in the community in relation to the implementation of this PEP.
+Some aspects described below will be relevant even before the PEP is fully
+implemented in packaging tools as there are some preparations that can be done
+in advance of this implementation to facilitate any potential transition later
+on. The groups covered below are:
+
+- `Package end users`_
+- `Package authors`_
+- `Packaging repository maintainers`_
+
+Package end users
+-----------------
+
+Package users should be provided with clear installation instructions that show
+what extras are available for packages and how they behave, for example
+explaining that by default some recommended dependencies or a given frontend or
+backend will be installed, and how to opt out of this or override defaults,
+depending what is available.
+
 Package authors
 ---------------
 
@@ -707,17 +727,8 @@ therefore need to carefully consider a migration plan, coordinating with the
 authors of ``package2``.
 
 
-Package users
--------------
-
-Package users should be provided with clear installation instructions that show
-what extras are available for packages and how they behave, for example
-explaining that by default some recommended dependencies or a given frontend or
-backend will be installed, and how to opt out of this or override defaults,
-depending what is available.
-
-Repackagers of Python libraries
--------------------------------
+Packaging repository maintainers
+--------------------------------
 
 The impact on individuals who repackage Python libraries for different
 distributions, such as `conda <https://docs.conda.io>`_, `Homebrew