systemd: finally add oomd configuration

etc/systemd/oomd.conf.d/20-oomd.conf

@@ -0,0 +1,11 @@
+[OOM]
+# Default values from ../oomd.conf during systemd 255 (255.10-1.fc40),
+# but remember to read man oomd.conf
+#SwapUsedLimit=90%
+DefaultMemoryPressureLimit=60%
+DefaultMemoryPressureDurationSec=30s
+# I question 90 % being enough and healthy battery charging also uses 80 %,
+# so let's try this since I prioritise not freezing over max utilization.
+SwapUsedLimit=80%
+#DefaultMemoryPressureLimit=
+#DefaultMemoryPressureDurationSec=