Fix typographical errors in README.md

Per [Cambridge Dictionary](https://dictionary.cambridge.org/grammar/british-grammar/it-s-or-its), `it's` is reserved for `it is` or `it has`, but in this context it is being used as neither of those.

README.md

@@ -8,7 +8,7 @@
     <img align=center src="https://github.com/communitycenter/stardew.app/blob/main/.github/background.png?raw=true" alt="Stardew.app Logo" width="500" /></br>
 </p>
 
-The website uses [Next.js](https://nextjs.org) for it's frontend, [PlanetScale](https://planetscale.com) for it's database, and a mixture of TypeScript and Python scripts to supplement data into the website. Internally, we use [Linear](https://linear.app) and [Pierre](https://pierre.co) for issue tracking and branch management.
+The website uses [Next.js](https://nextjs.org) for its frontend, [PlanetScale](https://planetscale.com) for its database, and a mixture of TypeScript and Python scripts to supplement data into the website. Internally, we use [Linear](https://linear.app) and [Pierre](https://pierre.co) for issue tracking and branch management.
 
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