Improve where docstring

[dsaxton]

A couple small fixes to the where docstring, also making an example a bit more clear.

[WillAyd]

Changes look good I think failures are from a flaky test so restarted

[codecov]

Codecov Report

Merging #26018 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26018      +/-   ##
==========================================
- Coverage   91.82%   91.81%   -0.01%     
==========================================
  Files         175      175              
  Lines       52551    52551              
==========================================
- Hits        48256    48252       -4     
- Misses       4295     4299       +4

Flag	Coverage Δ
#multiple	90.38% <ø> (ø)	⬆️
#single	40.72% <ø> (-0.14%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	93.54% <ø> (ø)	⬆️
pandas/io/gbq.py	75% <0%> (-12.5%)	⬇️
pandas/core/frame.py	96.79% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26018 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26018      +/-   ##
==========================================
- Coverage   91.82%   91.81%   -0.01%     
==========================================
  Files         175      175              
  Lines       52551    52551              
==========================================
- Hits        48256    48252       -4     
- Misses       4295     4299       +4

Flag	Coverage Δ
#multiple	90.38% <ø> (ø)	⬆️
#single	40.72% <ø> (-0.14%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	93.54% <ø> (ø)	⬆️
pandas/io/gbq.py	75% <0%> (-12.5%)	⬇️
pandas/core/frame.py	96.79% <0%> (-0.12%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a1fee91...fd29fc7. Read the comment docs.

[WillAyd]

Thanks @dsaxton