Update the package description.

Recommend build-depending on the new sphinx virtual package.

debian/changelog

@@ -8,6 +8,8 @@ sphinx (3.0.4-1) UNRELEASED; urgency=medium
     - autodoc_skip_mocked.diff
   * Refresh and rebase other patches.
   * Update numbers in debian/jstest/run-tests for the new release.
+  * Update the package description.
+    - Recommend build-depending on the new sphinx virtual package.
 
  -- Dmitry Shachnev <mitya57@debian.org>  Mon, 01 Jun 2020 15:18:17 +0300
 

debian/control

@@ -66,7 +66,7 @@ Breaks: python3-breathe (<< 4.13),
         python3-sphinx-celery (<< 2.0.0),
         python3-sphinxcontrib.websupport (<< 1.1.2)
 Conflicts: python-sphinx
-Description: documentation generator for Python projects (implemented in Python 3)
+Description: documentation generator for Python projects
  Sphinx is a tool for producing documentation for Python projects, using
  reStructuredText as markup language.
  .
@@ -79,7 +79,9 @@ Description: documentation generator for Python projects (implemented in Python
     - automatic testing of code snippets,
     - including docstrings from Python modules.
  .
- This package includes Python 3 modules.
+ Build-depend on sphinx if your package uses /usr/bin/sphinx-*
+ executables. Build-depend on python3-sphinx if your package uses
+ the Python API (for instance by calling python3 -m sphinx).
 
 Package: sphinx-common
 Architecture: all