DOC: inline comments on tk, pygobject, and wxPython

Author: tacaswell

doc/devel/dependencies.rst

@@ -41,12 +41,19 @@ Matplotlib figures can be rendered to various user interfaces. See
 :ref:`what-is-a-backend` for more details on the optional Matplotlib backends
 and the capabilities they provide.
 
-* Tk_ (>= 8.4, != 8.6.0 or 8.6.1) [#]_: for the Tk-based backends.
+* Tk_ (>= 8.4, != 8.6.0 or 8.6.1): for the Tk-based backends. Tk is part of
+  most standard Python installations, but it's not part of Python itself and
+  thus may not be present in rare cases.
 * PyQt6_ (>= 6.1), PySide6_, PyQt5_, or PySide2_: for the Qt-based backends.
-* PyGObject_: for the GTK-based backends [#]_.
+* PyGObject_: for the GTK-based backends. If using pip (but not conda or system
+  package manager) PyGObject must be built from source; see `pygobject
+  documentation
+  <https://pygobject.readthedocs.io/en/latest/devguide/dev_environ.html>`_.
 * pycairo_ (>= 1.11.0) or cairocffi_ (>= 0.8): for the GTK and/or cairo-based
   backends.
-* wxPython_ (>= 4) [#]_: for the wx-based backends.
+* wxPython_ (>= 4): for the wx-based backends.  If using pip (but not conda or
+  system package manager) on Linux wxPython wheels must be manually downloaded
+  from https://wxpython.org/pages/downloads/.
 * Tornado_ (>=5): for the WebAgg backend.
 * ipykernel_: for the nbagg backend.
 * macOS (>=10.12): for the macosx backend.
@@ -63,13 +70,6 @@ and the capabilities they provide.
 .. _Tornado: https://pypi.org/project/tornado/
 .. _ipykernel: https://pypi.org/project/ipykernel/
 
-.. [#] Tk is part of most standard Python installations, but it's not part of
-       Python itself and thus may not be present in rare cases.
-.. [#] If using pip (and not conda), PyGObject must be built from source; see
-       https://pygobject.readthedocs.io/en/latest/devguide/dev_environ.html.
-.. [#] If using pip (and not conda) on Linux, wxPython wheels must be manually
-       downloaded from https://wxpython.org/pages/downloads/.
-
 Animations
 ~~~~~~~~~~