Update docs to reflect that Sage is in Debian now.

debian/cantor-backend-sage.README.Debian

 Sage backend for Cantor for Debian
 ----------------------------------
 
-At the moment, Sage is not available in Debian, so you need to manually
-install it for making cantor-backend-sage useful.
+At the moment, Sage is not available in Debian except for a few architectures,
+so you may need to manually install it for making cantor-backend-sage useful.
 Cantor will use Sage automatically if the `sage' executable is in $PATH
 (so `which sage' returns its path); if it is not, you can set the path to the
 locally installed `sage' in the preferences of the Sage backend of Cantor.

debian/changelog

@@ -3,6 +3,7 @@ cantor (4:20.12.1-4) UNRELEASED; urgency=medium
   [ John Scott ]
   * Patch the Sage backend to work around issue in the SageMath package.
     (Addresses: #972346)
+  * Update docs to reflect that Sage is in Debian now. (Closes: #980318)
 
  -- Debian Qt/KDE Maintainers <debian-qt-kde@lists.debian.org>  Sun, 17 Jan 2021 18:34:54 -0500
 

debian/control

@@ -241,9 +241,6 @@ Description: Sage backend for Cantor
  This package provides the backend for using the Sage Mathematics Software
  (https://www.sagemath.org) in Cantor.
  .
- Please note that sagemath is not available in Debian, so you need to manually
- install it for this package to work.
- .
  This package is part of the KDE education module.
 
 Package: cantor-backend-scilab