twitter img alternate added

Author: Avinash

packages/docs/src/components/head.js

@@ -15,6 +15,7 @@ export const Head = ({title, description}) =>{
             <meta name="twitter:title" content={title} />
             <meta name="twitter:description" content={description} />
             <meta name="twitter:image" content="https://user-images.githubusercontent.com/1863771/76433547-c0e94e80-63b4-11ea-9cca-c859226e5021.png" />
+            <meta name="twitter:image:alt" content="React-ui" />
 
             {/* facebook */}
             <meta property="og:type" content="website" />