[DOCS] "Contributing" page sets unrealistic expectations

Description
The CONTRIBUTING page claims that PRs with test cases will generally receive some kind of response the same business day, and sometimes even been merged that day.

Suggested Fix
The documentation should be updated to reflect the kind of response that contributors should expect, rather than presenting such an optimistically ambitious standard.

Also, what is the preferred way of kicking loose an issue that seems to have fallen through the cracks? How long should one wait before pinging an assigned reviewer if we haven't heard from them?

Type of documentation
CONTRIBUTING guide.

Location or format of documentation
https://github.com/saltstack/salt/blob/master/CONTRIBUTING.rst#now-what

Additional context
n/a