Update README.md

joinmisskey.github.io -> join.misskey.page

README.md

@@ -13,7 +13,7 @@
 <a href="https://misskey.io">Misskey</a> is a decentralized microblogging platform born on Earth.
 Since it exists within the Fediverse (a universe where various social media platforms are organized),
 it is mutually linked with other social media platforms.
-Why don't you take a short break from the hustle and bustle of the city, and dive into a new Internet? <a href="https://joinmisskey.github.io/">Find an instance!</a>
+Why don't you take a short break from the hustle and bustle of the city, and dive into a new Internet? <a href="https://join.misskey.page/">Find an instance!</a>
 </p>
 
 <a href="https://www.patreon.com/syuilo"><img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" alt="Become a Patron!" width="160" /></a>