Add benchmark results to README

[chshersh]

Hi, thanks for writing this library! I was interested in using the fastest function to get monotonic time to measure performance and fund this wonderful library ✨

The library itself provides several functions to get the time and I was wondering which one is the fastest. I see that the library has benchmarks. Since benchmarks use criterion, I had to wait half an hour on my old laptop to compile them and run. So I propose to add some benchmark results to README so users can quickly compare different functions and select the best one 🤗

benchmarking getTime/Monotonic
time                 53.79 ns   (53.70 ns .. 53.95 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 53.82 ns   (53.72 ns .. 54.13 ns)
std dev              551.6 ps   (210.6 ps .. 1.082 ns)

benchmarking getTime/Realtime
time                 53.44 ns   (53.24 ns .. 53.70 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 53.32 ns   (53.25 ns .. 53.49 ns)
std dev              362.8 ps   (183.6 ps .. 634.4 ps)

benchmarking getTime/ProcessCPUTime
time                 581.8 ns   (575.6 ns .. 591.8 ns)
                     0.999 R²   (0.997 R² .. 1.000 R²)
mean                 578.0 ns   (575.9 ns .. 585.9 ns)
std dev              11.07 ns   (2.941 ns .. 24.00 ns)
variance introduced by outliers: 23% (moderately inflated)

benchmarking getTime/ThreadCPUTime
time                 563.6 ns   (563.3 ns .. 564.2 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 564.3 ns   (564.0 ns .. 564.9 ns)
std dev              1.507 ns   (946.2 ps .. 2.239 ns)

benchmarking getTime/MonotonicRaw
time                 53.99 ns   (53.88 ns .. 54.22 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 54.00 ns   (53.89 ns .. 54.35 ns)
std dev              595.9 ps   (122.4 ps .. 1.251 ns)
variance introduced by outliers: 11% (moderately inflated)

benchmarking getTime/Boottime
time                 53.32 ns   (53.23 ns .. 53.45 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 53.27 ns   (53.23 ns .. 53.35 ns)
std dev              180.4 ps   (105.4 ps .. 283.9 ps)

benchmarking getTime/MonotonicCoarse
time                 52.07 ns   (48.18 ns .. 57.83 ns)
                     0.947 R²   (0.927 R² .. 0.975 R²)
mean                 55.50 ns   (52.11 ns .. 59.87 ns)
std dev              13.31 ns   (10.18 ns .. 19.63 ns)
variance introduced by outliers: 98% (severely inflated)

benchmarking getTime/RealtimeCoarse
time                 45.10 ns   (44.40 ns .. 46.09 ns)
                     0.973 R²   (0.950 R² .. 0.989 R²)
mean                 56.50 ns   (51.38 ns .. 64.96 ns)
std dev              23.29 ns   (17.33 ns .. 30.06 ns)
variance introduced by outliers: 100% (severely inflated)

benchmarking GHC.Clock.getMonotonicTimeNSec
time                 22.75 ns   (22.62 ns .. 22.92 ns)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 22.65 ns   (22.61 ns .. 22.74 ns)
std dev              197.3 ps   (102.5 ps .. 355.4 ps)