Add the location of the octopus configure script in lmod file

Add the location of the octopus configure script in lmod file (MPSD_OCTOPUS_CONFIGURE)

README.rst

@@ -177,6 +177,24 @@ Requirements for particular toolchains and package sets
 - ``foss*-mpi`` currently needs linux header files installed (to compile the ``knem`` package)
 - ``foss*-cuda-mpi`` (proably as `*-mpi, needs testing TODO`)
 
+Finding the Octopus configure script
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For each Octopus toolchain, there is a Octopus configure script available. Once the
+toolchain is loaded, the variable ``$MPSD_OCTOPUS_CONFIGURE`` contains that
+path. The path can also be seen using the ``module show TOOLCHAINNAME`` command. For example::
+
+  $ mpsd-software install dev-23a foss2022a-mpi
+  $ module use /home/fangohr/mpsd-software-manager/dev-23a/cascadelake/lmod/Core
+  $ module show toolchains/foss2022a-mpi
+  ...
+  depends_on("cgal/5.0.3")
+  depends_on("hdf5/1.12.2")
+  setenv("MPSD_OCTOPUS_CONFIGURE","/home/fangohr/mpsd-software/dev-23a/spack-environments/octopus/foss2022a-mpi-config.sh")
+  $ module load toolchains/foss2022a-mpi
+  $ echo $MPSD_OCTOPUS_CONFIGURE
+  /home/fangohr/mpsd-software/dev-23a/spack-environments/octopus/foss2022a-mpi-config.sh
+
 
 Working example
 ~~~~~~~~~~~~~~~