Mitigating dependency on read the docs by giving instructions for building the manual from the mps tree <https://github.com/ravenbrook/mps/pull/141#issuecomment-1413166615>.

mps/manual/build.txt

@@ -9,7 +9,7 @@ Introduction
 ------------
 
 This document describes the various ways in which you can build the MPS,
-its libraries, and the tests and tools that come with it.
+its manual, its libraries, and the tests and tools that come with it.
 
 You may be building the MPS for a number of different purposes.
 
@@ -94,6 +94,30 @@ If you want to do anything beyond these simple cases, use the MPS build
 as described in the section "Building the MPS for development" below.
 
 
+Building the MPS manual
+-----------------------
+
+Builds of the MPS manual from the main MPS repo should be available at
+`<https://memory-pool-system.readthedocs.io/>`_.
+
+If that's not available, or if you have a variant of the MPS Kit, or
+are making modifications to the MPS itself, then you should build the
+manual for yourself.  This uses Sphinx
+`<https://www.sphinx-doc.org/>`_.
+
+On Unix-like platforms (including macOS), the Makefile in the manual
+directory can fetch and install a local copy of Sphinx and build the
+manual, like this::
+
+  cd manual
+  make html
+
+On Windows platforms, follow the `Sphinx installation instructions
+<https://www.sphinx-doc.org/en/master/usage/installation.html>`_ for
+Windows, then invoke Sphinx as shown in the Makefile in the manual
+directory.
+
+
 Building the MPS for development
 --------------------------------
 

mps/readme.txt

@@ -42,7 +42,8 @@ Getting started
 The MPS Kit is a complete set of sources and documentation to enable
 you to use, modify, and adapt the MPS: source code, manuals,
 procedures, design documentation, and so on.  See the manual_ for an
-index.
+index.  (If for some reason the manual_ isn't available, you can build
+it.  See below.)
 
 .. _manual: https://memory-pool-system.readthedocs.io/
 
@@ -55,8 +56,9 @@ using it.  The basic case is straightforward on supported platforms
     cl /O2 /c mps.c     Windows (with Microsoft SDK or Visual Studio 2010)
 
 This will produce an object file you can link with your project.  For
-details of how to configure the MPS, build libraries and tests, use
-IDEs, autoconf, etc. see `Building the MPS <manual/build.txt>`__.
+details of how to configure the MPS, build the manual, libraries and
+tests, use IDEs, autoconf, etc. see `Building the MPS
+<manual/build.txt>`__.
 
 For an example of using the MPS, see the `Scheme interpreter
 example <example/scheme/>`_.