add GitHub sponsors link

.github/FUNDING.yml

@@ -1,4 +1,5 @@
 # This file is for GitHub's sponsor button.
 # If you like my work and want to say more than thanks, feel free to buy me a coffee, a gift, or send a tip!
+github: SethClydesdale
 ko_fi: sethc95
 custom: ['https://sethclydesdale.github.io/tobira-study-resources/donate/']

donate/index.html

@@ -46,6 +46,7 @@ <h2 class="title center" id="donate">Donate</h2>
         <p>Tobira Study Resources was created by <a href="https://github.com/SethClydesdale">Seth Clydesdale</a>, with the goal of making self-study with the Tobira textbooks easier for everyone, for free. As an open source developer, my only source of income for my works are donations. So if you found this project helpful and would like to support my work, please see below for the different ways that you can contribute.</p>
 
         <ul style="font-size:14px;">
+          <li>Sponsor me on <a href="https://github.com/sponsors/SethClydesdale"><strong>GitHub</strong></a>.</li>
           <li>Send me a tip via <a href="https://paypal.me/sethc95/"><strong>PayPal</strong></a>.</li>
           <li>Buy me a coffee via <a href="https://ko-fi.com/sethc95"><strong>Ko-fi</strong></a>.</li>
           <li>Buy me a gift from my Amazon Wishlist: <a href="https://www.amazon.com/hz/wishlist/ls/S7YILFHYK0IZ"><strong>US</strong></a> | <a href="https://www.amazon.jp/hz/wishlist/ls/31FKBIJPAGBAL"><strong>JP</strong></a>.</li>