Fix spelling & grammar in documentation

[kaitj]

Proposed changes

Fixes a few mistakes found in the documentation with regards to spelling, duplicate words and grammar.

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you are unsure about any of the choices, don't hesitate to ask!

• Changes have been tested to ensure that fix is effective or that a feature works.
• Changes pass the unit tests
• Code has been run through the poe quality task
• I have included necessary documentation or comments (as necessary)
• Any dependent changes have been merged and published

Notes

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