doc: explain adding and updating software

README.org

@@ -39,3 +39,30 @@ installed on the cluster.  Installation paths are configured in
 Each installed software has an accompanying module file. They are
 separated in ~guix~ (for FOSS software) and ~prop~ (for proprietary
 software).
+
+* Updating software
+
+1. Optional: Prepare the installation files by repacking it (into
+   another format)
+2. Add a new entry in [[cluster_config/software.yaml][software.yaml]] under the corresponding software
+   key (e.g. ~matlab~), necessary entries are ~version~, ~prefix~,
+   ~source~ and ~executable~ (only if slurm submission support is
+   needed in [[https://gitlab.ost.ch/scl/slurm-submit][slurm-submit]])
+3. Copy the installation binaries onto the cluster according to the
+   value ~asset_path~ in file [[cluster_config/installation.yaml][installation.yaml]] the variable ~prefix~
+   and the ~source~ path in [[cluster_config/software.yaml][software.yaml]]
+4. Run the ~install_software.yaml~ file according to chapter
+   [[Installing software]]
+
+* Adding new software
+
+1. Add a new task in the ~tasks~ list in file ~install_software.yaml~
+   with the ~name~: ~Install <software>~
+2. Create a new file ~install_<software>.yaml~ with the detailed
+   instructions for installation of this software (copy from an
+   existing script)
+3. Create a new entry in the file [[cluster_config/software.yaml][software.yaml]] with a new key
+   ~<software>~
+4. Go to chapter [[Updating software]] and follow this steps
+
+