Correct typo and add further description

Co-authored-by: sfmig <[email protected]>

Author: matt-graham

benchmarks/README.md

@@ -1,6 +1,14 @@
 # Benchmarks for `s2fft`
 
-Scripts for benchmarking `ss2ft` with `timeit` (and optionally `memory_profiler`).
+Scripts for benchmarking `s2fft` with `timeit` (and optionally `memory_profiler`).
+
+Measures time to compute transforms for grids of parameters settings, optionally 
+outputting the results to a JSON file to allow comparing performance over versions
+and/or systems. 
+If the [`memory_profiler` package](https://github.com/pythonprofilers/memory_profiler) 
+is installed an estimate of the peak (main) memory usage of the benchmarked functions
+will also be recorded.
+
 
 ## Description