docs/reference/micropython2_migration: Add migration guide.

This is just scaffolding for now, but the idea is that there should be an
addition to this file for every commit that uses the
`MICROPY_PREVIEW_VERSION_2` macro.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/reference/index.rst

@@ -31,3 +31,4 @@ implementation and the best practices to use them.
    asm_thumb2_index.rst
    filesystem.rst
    pyboard.py.rst
+   micropython2_migration.rst

docs/reference/micropython2_migration.rst

@@ -0,0 +1,74 @@
+.. _micropython2_migration:
+
+MicroPython 2.0 Migration Guide
+===============================
+
+MicroPython 2.0 is the (currently in development, not yet available) next major
+release of MicroPython.
+
+After maintaining API compatibility for almost a decade with the ``1.x`` series, in
+order to unblock some project-wide improvements MicroPython 2.0 will introduce a
+small number of breaking API changes that will require some programs to be
+updated. This guide explains how to update your Python code to accommodate these
+changes.
+
+This document is a work-in-progress. As more work is done on MicroPython 2.0,
+more items will be added to the lists below.
+
+**Note:** There are currently no MicroPython 2.0 firmware builds available for
+download. You can build it yourself by enabling the ``MICROPY_PREVIEW_VERSION_2``
+config option. As it gets closer to being ready for release, builds will be
+provided for both ``1.x.y`` and ``2.0.0-preview``.
+
+Hardware and peripherals
+------------------------
+
+Overview
+~~~~~~~~
+
+The goal is to improve consistency in the :mod:`machine` APIs across different
+ports, making it easier to write code, documentation, and tutorials that work on
+any supported microcontroller.
+
+This means that some ports' APIs need to change to match other ports.
+
+Changes
+~~~~~~~
+
+*None yet*
+
+OS & filesystem
+---------------
+
+Overview
+~~~~~~~~
+
+The primary goal is to support the ability to execute :term:`.mpy files <.mpy
+file>` directly from the filesystem without first copying them into RAM. This
+improves code deployment time and reduces memory overhead and fragmentation.
+
+Additionally, a further goal is to support a more flexible way of configuring
+partitions, filesystem types, and options like USB mass storage.
+
+Changes
+~~~~~~~
+
+*None yet*
+
+CPython compatibility
+---------------------
+
+Overview
+~~~~~~~~
+
+The goal is to improve compatibility with CPython by removing MicroPython
+extensions from CPython APIs. In most cases this means moving existing
+MicroPython-specific functions or classes to new modules.
+
+This makes it easier to write code that works on both CPython and MicroPython,
+which is useful for development and testing.
+
+Changes
+~~~~~~~
+
+*None yet*