Merge pull request matplotlib#16720 from anntzer/dqh

Download qhull at build-or-sdist time.

Author: jklymak

.gitignore

@@ -105,3 +105,5 @@ lib/z.lib
 #########################
 lib/matplotlib/backends/web_backend/node_modules/
 lib/matplotlib/backends/web_backend/package-lock.json
+
+LICENSE/LICENSE_QHULL

INSTALL.rst

@@ -220,13 +220,15 @@ etc., you can install the following:
 FreeType and Qhull
 ------------------
 
-Matplotlib depends on `FreeType <https://www.freetype.org/>`_ (>=
-2.3), a font rendering library, and on `Qhull
-<http://www.qhull.org/>`_ (>= 2015.2), a library for computing
-triangulations.  By default (except on AIX) Matplotlib downloads and
-builds its own copy of FreeType (this is necessary to run the test
-suite, because different versions of FreeType rasterize characters
-differently), and uses its own copy of Qhull.
+Matplotlib depends on FreeType_ (>= 2.3), a font rendering library, and on
+Qhull_ (>= 2020.2), a library for computing triangulations.  By default,
+Matplotlib downloads and builds its own copies of FreeType (this is necessary
+to run the test suite, because different versions of FreeType rasterize
+characters differently) and of Qhull.  As an exception, Matplotlib defaults to
+the system version of FreeType on AIX.
+
+.. _FreeType: https://www.freetype.org/
+.. _Qhull: http://www.qhull.org/
 
 To force Matplotlib to use a copy of FreeType or Qhull already installed in
 your system, create a :file:`setup.cfg` file with the following contents: