README: more benchmark info

README.md

@@ -51,6 +51,16 @@ The benchmarks compare three mutex implementations:
  [`semaphore.Weighted`](https://pkg.go.dev/golang.org/x/sync/semaphore); it
  exists only in the test code, as a comparison baseline.
 
+What conclusions can be drawn from the results below? Well, `fifomu.Mutex`
+is always at least 1.5x slower than `sync.Mutex`, and often more. The
+worst results are in `BenchmarkMutexSpin`, where `fifomu.Mutex` is 10x slower
+than `sync.Mutex`.
+
+Benchmark your own workload before committing to `fifomu.Mutex`. In many
+cases you will be able to design around the need for FIFO lock acquisition.
+It's a bit of a code smell to begin with, but sometimes it's the most
+straightforward solution.
+
 ```
 $ GOMAXPROCS=10 go test -bench .
 goos: darwin