Add a line to import ImmutableMap for lesson01 readme

[ackerleytng]

Would be great if you could add a line to import ImmutableMap

import com.google.common.collect.ImmutableMap;

to help newbies!

[yurishkuro]

would you like to create a pull request?

[ackerleytng]

I can add it later!

Just realized this tutorial is based on com.uber.jaeger, which has now been replaced by io.jaegertracing. I'm trying to get io.jaegertracing working first.