Clarify autoscale parameter description

[normandy7]

Before submitting checklist

• Did you update the CHANGELOG? (not for test updates, internal changes/refactors or CI/CD setup)
• Did you ask the docs owner to review all the user-facing changes?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.03%. Comparing base (c4166f5) to head (80ed44c).

Additional details and impacted files

@@             Coverage Diff             @@
##           dev/1.x    #1742      +/-   ##
===========================================
- Coverage    75.04%   75.03%   -0.01%     
===========================================
  Files          304      304              
  Lines        15050    15050              
===========================================
- Hits         11294    11293       -1     
- Misses        3756     3757       +1     

Flag	Coverage Δ
macos	74.71% <ø> (-0.05%)	⬇️
py3.7	75.03% <ø> (-0.01%)	⬇️
ubuntu	74.90% <ø> (-0.01%)	⬇️
unit	75.03% <ø> (-0.01%)	⬇️
windows	73.95% <ø> (ø)

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