Fix typo in README.md

[adr-h]

What does this do / why do we need it?

Fixes a typo in the README.md. Not something high priority at all, just something that was bugging me.

What should your reviewer look out for in this PR?

Nothing technical, since no code was actually changed.

Do you need help or clarification on anything?

Not particularly.

Which issue(s) does this PR fix?

A typo in README.md. Not something high priority at all, just something that was bugging me.

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[adr-h]

I signed it!

[googlebot]

CLAs look good, thanks!

[darkowlzz]

Thanks for correcting that.