Add missing files to git.

Author: zzzFelix

src/components/BetaAlert.js

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+import React from 'react';
+
+const BetaAlert = () => (
+    <div class="alert alert-warning beta-alert" role="alert">
+        You are looking at preliminary documentation for secureCodeBox v2 beta. Not what you want? See <a
+            href="https://github.com/secureCodeBox/secureCodeBox/blob/master/README.md"
+            class="alert-link"
+            rel="noreferrer"
+            target="_blank">
+                latest stable release documentation
+        </a>.
+    </div>
+);
+
+export default BetaAlert;

src/scss/components/_beta-alert.scss

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+.beta-alert {
+    text-align: center;
+    margin: 0;
+}