suggest to remove the default parameter frequency to avoid (my) confusion, add data dictionary information to example

[Oliver-Prislan]

Dear Sirs,

I like your tool to read eso files.

As the variable finder didn't work initially (I didn't have timestep but hourly data)
I found you are using frequency defaulted to timestep in the find_variable function call.
I suggest to remove this default.

Secondly, as I was unaware of the data dictionary, I wrote my own variable name extractor.
This was a waste of time as your dd is much easier to use (but not well documented)
I suggest to give an example - as you did for in the readme.

Thank you
the reader really eases my day