Docs: "Positive Slack" not defined in RTIO.rst

[drewrisinger]

Summary

The RTIO doc is missing a definition for "positive slack", though the term is used. Negative slack is defined on line 167.

Proposed Change

Suggested definition: (i.e. set timeline cursor now greater than the current wall clock rtio_counter)
This definition should be added to Line 169 of RTIO doc, right after the use of positive slack

Reasoning

This should be defined here because this is the first doc most users will read, and it is used extensively in the RTIO Reset section. While it seems trivial, this is a crucial concept and lack of clarity can affect understanding later on when using or developing software for ARTIQ.

[jordens]

But it says (in L118) RTIO slack is the difference between timeline cursor and wall clock time (now - rtio_counter). right when slack is mentioned the first time. That directly implies that positive slack is equivalent to now > rtio_counter. You are correct, this is a crucial concept. What do you propose?