src/doc/en/developer/packaging_sage_library.rst: Mention relint, sage --fiximports

Author: Matthias Koeppe

src/doc/en/developer/packaging_sage_library.rst

@@ -274,6 +274,10 @@ distribution -- which then must be declared as a run-time dependency.
   the ``sage:`` prompt. In particular, no Sage library code should import from
   :mod:`sage.rings.all`.
 
+  To audit the Sage library for such imports, use ``sage --tox -e relint``.
+  In most cases, the imports can be fixed automatically using the
+  tool ``sage --fiximports``.
+
 - Replace module-level imports by method-level imports.  Note that
   this comes with a small runtime overhead, which can become
   noticeable if the method is called in tight inner loops.