"Memory Usage" README

[iztsv]

Hello!

README contains the following:

Average Memory Usage
In Megabyte.

avg(nodejs_external_memory_bytes / 1024) by (service)

but nodejs_external_memory_bytes is size in bytes, therefore, we need use avg(nodejs_external_memory_bytes / 1024 / 1024) in order to show size in megabytes?

[Shadowbeetle]

Thanks! Fixed it.