Issues with split_fastx command using pomoxis assem_assembly

[tweilin]

Hi, I had an issue regarding the use of assem_assembly command using the medaka_walkthrough (https://github.com/nanoporetech/medaka/blob/master/docs/walkthrough.rst)

Run into error where the command split_fastx was not found even though the script has it. No idea on how to troubleshoot this issue.