build/pkgs/{r,rpy2}: Explain dummy / pseudo-standard package type

build/pkgs/r/SPKG.rst

@@ -24,3 +24,14 @@ Upstream Contact
 
 -  https://www.r-project.org
 -  R mailing list, #R in IRC
+
+
+Special Installation Instructions
+---------------------------------
+
+In the Sage distribution, ``r`` is a "dummy" package:
+It is here to provide information about equivalent system packages.
+R cannot be installed using the Sage distribution.
+Please install it manually, either using one of the system package
+commands shown here or following the upstream instructions
+at https://www.r-project.org

build/pkgs/rpy2/SPKG.rst

@@ -12,21 +12,16 @@ License
 -------
 
 -  GPL 2+
--  Note that we have deleted references to Mozilla PL as an option,
-   which we are allowed to do by the full rpy2 license in order to
-   remain GPL-compatible
-
 
 Upstream Contact
 ----------------
 
--  https://rpy2.bitbucket.io
+- https://github.com/rpy2/rpy2
 
-Special Update/Build Instructions
+Special Installation Instructions
 ---------------------------------
 
-Patches
-~~~~~~~
-
--  setup.patch: takes care of a few parsing issues.
--  cygwin.patch: let rpy2 build on Cygwin.
+In the Sage distribution, ``rpy2`` is a "semi-standard" package: It will be
+automatically installed by the Sage distribution if a suitable system
+installation of R is detected by ``configure``. (Note that Sage no longer
+ships and installs its own copy of R.)