Add GitHub logo (#335)

Author: github-actions[bot]

css/main.css

@@ -1244,7 +1244,7 @@ pre code {
   vertical-align: middle;
 }
 .links-of-author a::before {
-  background: #2d3983;
+  background: #a28a59;
   display: inline-block;
   margin-right: 3px;
   transform: translateY(-2px);

funding/images/github.png

@@ -31,6 +31,7 @@
 <meta property="og:image" content="https://symbioticlab.org/funding/images/ford.png">
 <meta property="og:image" content="https://symbioticlab.org/funding/images/cisco.png">
 <meta property="og:image" content="https://symbioticlab.org/funding/images/google.png">
+<meta property="og:image" content="https://symbioticlab.org/funding/images/github.png">
 <meta property="og:image" content="https://symbioticlab.org/funding/images/slalom.png">
 <meta property="og:image" content="https://symbioticlab.org/funding/images/vmware.png">
 <meta property="og:image" content="https://symbioticlab.org/funding/images/salesforce.png">
@@ -166,7 +167,8 @@ <h2 id="current-sponsors">Current Sponsors<a class="headerlink" href="#current-s
 <img src="images/mozilla.png" alt="Mozilla" />
 <img src="images/ford.png" alt="Ford" />
 <img src="images/cisco.png" alt="Cisco" />
-<img src="images/google.png" alt="Google" /></p>
+<img src="images/google.png" alt="Google" />
+<img src="images/github.png" alt="GitHub" /></p>
 </div>
 <h2 id="past-sponsors">Past Sponsors<a class="headerlink" href="#past-sponsors"></a></h2>
 <div class='flex-row'>