comment on linux headers being needed

Small addition to README.rst

README.rst

@@ -161,7 +161,13 @@ The ``mpsd-software-manager`` python package.
   - Please check https://spack.readthedocs.io/en/latest/getting_started.html#system-prerequisites
 
 
-The compilation of the ``*-mpi`` toolchains needs linux headers installed. (TODO Add more detail.)
+Requirements for particular toolchains and package sets
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- ``foss*-serial`` should compile with the dependencies outlined above
+- ``foss*-mpi`` currently needs linux header files installed (to compile the ``kmem`` package)
+- ``foss*-cuda-mpi`` (proably as `*-mpi, needs testing TODO)
+
 
 Working example
 ~~~~~~~~~~~~~~~
@@ -171,3 +177,4 @@ compilation cycle (including compilation of Octopus). (TODO)
 
 
 
+