I use the following, which blocks the login page and forgot password page (because they usually contain the "?to=" parameter so you get duplicate content).
"qa/" here is the subfolder you have Q2A in - if you're using a root domain remove that bit.
# allow google image bot to search all images
Sitemap: Sitemap address
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July 15, 2020: Q2A 1.8.5 released!