Add a README that explains the FS project

README.md

+This project is a dummy project with issues imported from our
+old Flyspray bug tracker.
+
+You can continue discussion here and reference bugs from all other GitLab
+repositories by writing:
+
+```
+flyspray/FS#xyz
+```
+
+**Please do not open any new bugs in the flyspray project**,
+but instead file them under the correct core module.
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