Memory used is returned in MB, but README say bytes

[josmithua]

Reading HybridPerformanceToolkit.{kt,swift}, the memory usage is returned in megabytes, but the README says getMemoryUsage returns bytes.

[josmithua]

A separate but another docs issue - The README should be clear that getMemoryUsage and getCpuUsage return 0 on the first call.

[Nodonisko]

Hi, valid points will fix that.