Update help text for clarity: `dereplicate --p-mode super`

[mikerobeson]

This issue was initially discovered by a user in this thread. When a set of sequences, and their associated taxonomy:

• seq_01 k__Animalia;p__Arthropoda;c__Insecta;o__Hymenoptera;f__;g__;s__
• seq_02 k__Animalia;p__Arthropoda;c__Insecta;o__Hymenoptera;f__;g__;s__
• seq_03 k__Animalia;p__Arthropoda;c__Insecta;o__Coleoptera;f__Coccinellidae;g__Harmonia;s__Harmonia axyridis
• seq_04 k__Animalia;p__Arthropoda;c__Insecta;o__Coleoptera;f__Coccinellidae;g__Harmonia;s__Harmonia axyridis
• ...

are derepliated using --p-mode super, there is potential for achimeric taxonomy string to be produced:

• seq_02 k__Animalia;p__Arthropoda;c__Insecta;o__Hymenoptera;f__Coccinellidae;g__Harmonia;s__Harmonia axyridis

This chimeric taxonomy string does not exist in the taxonomy input file.

EDIT: the code is working as intended, as per this post.

EDIT 2: As per EDIT 1, I am changing the focus of this Issue to: clarify the help text for --p-mode super.