usecase: add description use cases

test-monitor/usecase/README.md

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+# Use cases 
+
+This part of the repopsitory contains use cases for the `orchestrator` and the `polena` real-time environment. A short description of the use cases follows below.
+
+## Use cases 1 and 2 - Real-Time image processing
+
+These two use cases relate to a production-line image processing scenario, -- pictures and more detailed description follow.
+
+*** WIP ***
+
+## Use case 3 - Codesys Control
+
+In this scenario we consider the run-time software for IEC61131-3 compliant Soft-PLCs in bare or virtualized settings
+
+*** WIP ***
+
+## Use case 4 - Simatic vPLC
+
+The fourth application considers the real-time environment around Siemens's vPLC package.
+
+*** WIP ***
+
+