ENH: Citing source in README file

[the-nose-knows]

For GH users who strictly or heavily use the web-view instead of a local Git, having a direct link is handy, as it does not require downloading the PDF if the user wanted to go to the source of it directly. It's an alternative that allows those interested in more uploads similar to this PDF from the same author(s).

• closes: N/A
• tests added / passed: N/A
• whatsnew: Added source of PDF to README file for the cheatsheet

[jorisvandenbossche]

You linked to the R cheatsheet (on which the pandas one is based). Was that on purpose?

[jreback]

actually I think this is reasonable, though I think the wording should be that this is referenced/based on the dplyr sheet.

[the-nose-knows]

@jorisvandenbossche Good catch! I've updated the file with a new commit.
@jreback feel free to word this to whatever is most appropriate. As long as the spirit of the PR is satisfied, I'm happy with whatever implementation is used.

[codecov]

Codecov Report

Merging #15856 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #15856      +/-   ##
==========================================
- Coverage   90.98%   90.97%   -0.02%     
==========================================
  Files         143      145       +2     
  Lines       49443    49483      +40     
==========================================
+ Hits        44985    45015      +30     
- Misses       4458     4468      +10

Flag	Coverage Δ
#multiple	88.73% <ø> (ø)	⬆️
#single	40.63% <ø> (-0.13%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/util/clipboard/windows.py	11.62% <0%> (-1.02%)	⬇️
pandas/io/common.py	69.33% <0%> (-0.93%)	⬇️
pandas/core/common.py	91.03% <0%> (-0.27%)	⬇️
pandas/computation/engines.py	88.88% <0%> (-0.18%)	⬇️
pandas/core/frame.py	97.56% <0%> (-0.1%)	⬇️
pandas/util/clipboard/clipboards.py	26.58% <0%> (ø)	⬆️
pandas/io/feather_format.py	86.66% <0%> (ø)	⬆️
pandas/_version.py	44.65% <0%> (ø)	⬆️
pandas/__init__.py	92.68% <0%> (ø)	⬆️
... and 20 more

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[jreback]

seems reasonable, thanks.