Clarify documentation for `antibody`

[adthrasher]

Description of the bug

The usage document describes the antibody column as:

Antibody name. This is required to segregate downstream analysis for different antibodies. Required when control is specified.

This should be updated to clarify that it is only specifiable when control is specified, not just required with the control column.

Command used and terminal output

Relevant files

No response

System information

No response