add FAQ about workload

docs/tutorial.md

@@ -298,6 +298,14 @@ If the true retention is significantly lower than your desired retention, try in
 
 ***
 
+Q19: Why my workload increases/decreases significantly after I switch to FSRS?
+
+A19: The workload depends on your retention:
+- If your true retention before switching to FSRS was significantly lower than your current desired retention, FSRS will let you review more frequently than before.
+- If your previous true retention was significantly higher than your current desired retention, FSRS will let you review less frequently.
+
+***
+
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