Added JSDoc for src/mixins/*

Signed-off-by: Matthew Nickson <mnickson@sidingsmedia.com>

src/mixins/theme.js

@@ -75,6 +75,7 @@ export default {
     },
 
     methods: {
+        /** Update the theme color meta tag */
         updateThemeColorMeta() {
             if (this.theme === "dark") {
                 document.querySelector("#theme-color").setAttribute("content", "#161B22");