[perf] Update README

perf/README.md

@@ -6,14 +6,22 @@ To build the benchmarks in this directory you need to set the benchmark
 option while configuring the build with meson:
 
 ```
-meson configure build -Dbenchmark=enabled --buildtype=release
+meson build -Dbenchmark=enabled --buildtype=release
+```
+or:
+```
+meson build -Dbenchmark=enabled --buildtype=debugoptimized
 ```
 
-Then build the benchmark binaries with ninja:
 
+Then build a specific benchmark binaries with ninja:
 ```
 ninja -Cbuild perf/benchmark-set
 ```
+or just build the whole project:
+```
+ninja -Cbuild
+```
 
 Finally, to run one of the benchmarks:
 
@@ -37,10 +45,10 @@ ninja -Cbuild
 Then run the benchmark with perf:
 
 ```
-perf record -g -o ~/tmp/profiles/subset.prof ./build/perf/benchmark-subset --benchmark_filter="BM_subset_codepoints/subset_notocjk/100000" --benchmark_repetitions=5
+perf record -g build/perf/benchmark-subset --benchmark_filter="BM_subset_codepoints/subset_notocjk/100000" --benchmark_repetitions=5
 ```
 You probably want to filter to a specific benchmark of interest and set the number of repititions high enough to get a good sampling of profile data.
 
 Finally view the profile with:
 
-perf report -i ~/tmp/profiles/subset.prof
+perf report