docs: fix subtle typos

[abiriadev]

Description of the change

This PR addresses several typos across the documentation (docs/*.md).

• Removed duplicated entries (in docs-using-js-api-support.md).
• Fixed obvious typos.
• And cleaned up trailing whitespaces.

That's all!

The whitespace changes were done automatically. If they are inappropriate or unnecessary, I will revert that part.

Why am I making this change?

I noticed a few typos while I was reading the documents.

Most of them are very subtle typos, but I also noticed some mistyped commands(e.g., git submodules), which should be fixed.

Checklist

• I've updated the default plugin import namespace and incremented the major version of javy-plugin-api if the QuickJS bytecode has changed.
• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli, javy-plugin, and javy-plugin-processing do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.

[saulecabrera]

Thanks!