DOC: Fixed minor spelling errors

[tommyod]

Two small changes:

• Two minor spelling errors corrected.
• Added part 7 of a tutorial series to the docs (parts 1-6 were included already, but not part 7).

[codecov]

Codecov Report

Merging #18941 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18941      +/-   ##
==========================================
- Coverage   91.59%   91.57%   -0.03%     
==========================================
  Files         150      150              
  Lines       48959    48959              
==========================================
- Hits        44843    44833      -10     
- Misses       4116     4126      +10

Flag	Coverage Δ
#multiple	89.93% <ø> (-0.03%)	⬇️
#single	41.13% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/plotting/_converter.py	65.22% <0%> (-1.74%)	⬇️
pandas/util/testing.py	84.9% <0%> (+0.21%)	⬆️

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[jorisvandenbossche]

thanks!

[tommyod]

Thanks for merging @jorisvandenbossche. I plan to read the docs carefully. If I find similar errors I will submit a PR.