Zipapp docs (#9356)

* Revert "README: Don't recommend using as a standalone script"

This reverts commit 9763bf65c6.

zipapps work fine now that we have a single entry point. Time to
recommend them again.

* update zipapp documentation to recommend the current packaging script

Also update the website documentation to mention this at all.

README.md

@@ -41,6 +41,14 @@ python3 -m pip install ninja
 More on Installing Meson build can be found at the
 [getting meson page](https://mesonbuild.com/Getting-meson.html).
 
+#### Creating a standalone script
+
+Meson can be run as a [Python zip
+app](https://docs.python.org/3/library/zipapp.html). To generate the
+executable run the following command:
+
+    ./packaging/create_zipapp.py --outfile meson.pyz --interpreter '/usr/bin/env python3' <source checkout>
+
 #### Running
 
 Meson requires that you have a source directory and a build directory

docs/markdown/Getting-meson.md

@@ -21,6 +21,17 @@ we strive to ensure that it will always be working and usable. All
 commits go through a pull-request process that runs CI and tests
 several platforms.
 
+### Packing Meson into a zipapp
+
+After downloading the release, you can create a standalone single-file
+executable for Meson by running the script:
+
+```
+./packaging/create_zipapp.py --outfile meson.pyz --interpreter '/usr/bin/env python3' <source checkout>
+```
+
+This uses python's native support for [zipapp].
+
 ## Installing Meson with pip
 
 Meson is available in the [Python Package Index] and can be installed
@@ -92,6 +103,7 @@ provide Python 3. Use either `mingw32/mingw-w64-i686-python3` or
 are building for.
 
   [GitHub release page]: https://github.com/mesonbuild/meson/releases
+  [zipapp]: https://docs.python.org/3/library/zipapp.html
   [Python Package Index]: https://pypi.python.org/pypi/meson/
   [Git]: https://github.com/mesonbuild/meson
   [Python's home page]: https://www.python.org/downloads/