Some grammar and clarity updates

[OliviaLynn]

Misc notes:

• Replacing performance testing plot image with a typo in the title
• I'm ambivalent to the actual case of the tutorial titles, would just prefer consistency (either all title case or all only-first-word-capitalized)

[github-actions]

Before [62cefb8]	After [5826ac3]	Ratio	Benchmark (Parameter)
15.3±0.2ms	15.7±0.2ms	1.02	benchmarks.time_box_filter_on_partition
98.4±1ms	98.5±1ms	1	benchmarks.time_kdtree_crossmatch
29.3±0.4ms	29.2±0.4ms	1	benchmarks.time_polygon_search
14.5±0.02s	14.4±0.02s	0.99	benchmarks.time_create_large_catalog
2.14±0.01s	2.12±0.01s	0.99	benchmarks.time_create_midsize_catalog

Click here to view all benchmarks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.67%. Comparing base (62cefb8) to head (dfcd209).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #482   +/-   ##
=======================================
  Coverage   97.67%   97.67%           
=======================================
  Files          39       39           
  Lines        1550     1550           
=======================================
  Hits         1514     1514           
  Misses         36       36           

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