README: add winget installation instructions (#627)

Author: arebee

README.md

@@ -48,6 +48,12 @@ $ age --decrypt -i key.txt data.tar.gz.age > data.tar.gz
             <code>port install age</code>
         </td>
     </tr>
+    <tr>
+        <td>Windows</td>
+        <td>
+            <code>winget install --id FiloSottile.age</code>
+        </td>
+    </tr>
     <tr>
         <td>Alpine Linux v3.15+</td>
         <td>