login: Specify spectator login is in beta.

static/styles/portico/portico_signin.css

@@ -716,6 +716,10 @@ html {
     button {
         /* Avoid excessive space at top of login form */
         margin-top: 0;
+
+        .spectator_beta_text {
+            color: hsl(0, 0%, 90%);
+        }
     }
 }
 

templates/zerver/login.html

@@ -38,6 +38,7 @@ page can be easily identified in it's respective JavaScript file. -->
                             <input type="hidden" name="next" value="{{ next }}" />
                             <button class="full-width">
                                 {{ _('Access without an account') }}
+                                <span class="spectator_beta_text">({{ _('Beta') }})</span>
                             </button>
                         </form>
                     </div>