Fix typos and linguistic errors in documentation / hacktoberfest

[survivant]

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It's not much, but I'm happy to help.

PS. I found also this some .md JSpdf instead of jspdf. It's when the sentence were starting, so it was uppercase, but it's the project's name, so it's look weird, but it could start by a lowercase because it's the official name of the project.

[HackbrettXXX]

Thanks!

[survivant]

if you want can you add this label to this PR : hacktoberfest-accepted