add alt text field

src/thread_page.eml.html

@@ -17,6 +17,9 @@ let f thread_view thread_id request =
 
         <label for="file" id="fileLabel" class="form-label">Picture:</label>
         <input id="file" name="file" aria-describedby="fileLabel" type="file" accept="image/*">
+
+        <label for="alt" id="altLabel" class="form-label">Image description:</label>
+        <input name="alt" type="text" class="form-control" id="alt" aria-labelledby="altLabel"></input>
       <button type="submit" class="btn btn-primary">Reply</button>
       </div>
     </form>