Update README.md

README.md

-# clusters
+# KSI/DSE clusters
 
-KSI clusters description, manual, and hints
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+We have two computational clusters **parlab** and **gpulab**.
+They are used for exercises, homework assignments, and research, where you need high-performance computing.
+The clusters are managed by the SLURM resource manager.
+Additionally, the Charliecloud is available on all worker nodes.
+
+> Do not execute any of your code on the front-end nodes directly, use worker nodes instead!
+
+All unknown terms (front-end node, worker node) will be explained later. Front-end nodes do not have installed any development software.