Show mod icon in Discord and Twitter embed (#29)

* show mod icon in embed

* Update README.md

* im done now

src/mods/[mod.id]/index.html

@@ -12,15 +12,15 @@
     <meta property="og:type" content="website">
     <meta property="og:title" content="$MOD_NAME - Geode">
     <meta property="og:description" content="View the $MOD_NAME mod for Geode">
-    <meta property="og:image" content="https://docs.geode-sdk.org/icon.png">
+    <meta property="og:image" content="$MOD_ICON_URL">
     <meta property="og:image:width" content="80">
     <meta property="og:image:height" content="80">
 
     <meta name="twitter:card" content="summary">
     <meta property="twitter:url" content="https://geode-sdk.org/mods/$MOD_ID">
     <meta name="twitter:title" content="$MOD_NAME - Geode">
     <meta name="twitter:description" content="View the $MOD_NAME mod for Geode">
-    <meta property="twitter:image:src" content="https://docs.geode-sdk.org/icon.png">
+    <meta property="twitter:image:src" content="$MOD_ICON_URL">
 
     <link href="/favicon.ico" rel="icon" type="image/x-icon">