[MRG] Fix docstring for dcmread

[scaramallion]

Describe the changes

Closes #1285

Tasks

• Documentation updated (if relevant)

[codecov]

Codecov Report

Merging #1287 (533039f) into master (fd168e5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1287   +/-   ##
=======================================
  Coverage   95.23%   95.23%           
=======================================
  Files          60       60           
  Lines        9515     9515           
=======================================
  Hits         9062     9062           
  Misses        453      453           

Impacted Files	Coverage Δ
pydicom/filereader.py	93.76% <ø> (ø)

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[scaramallion]

Pypy3 build failure due to this issue with setup-python action