add: multi OAuth2 option README.md, small cosmetic repairs

src/main/resources/templates/misc/flatten.html

@@ -25,7 +25,7 @@
                   <input type="checkbox" id="flattenOnlyForms" name="flattenOnlyForms">
                   <label for="flattenOnlyForms" th:text="#{flatten.flattenOnlyForms}" ></label>
                 </div>         
-                </div>	
+                </div>
                 <br>
                 <button type="submit" id="submitBtn" class="btn btn-primary" th:text="#{flatten.submit}"></button>
               </form>