Adjust alt to new Tails Greeter

wiki/src/doc/first_steps/startup_options.mdwn

@@ -49,7 +49,7 @@ Using <span class="application">Tails Greeter</span>
 appears after the <span class="application">Boot Loader Menu</span>, but before the
 <span class="application">GNOME Desktop</span>:
 
-[[!img tails-greeter-welcome-to-tails.png link=no alt="Welcome to Tails!"]]
+[[!img tails-greeter-welcome-to-tails.png link=no alt="Tails Greeter: Welcome to Tails!"]]
 
 You can activate assistive technologies, like a screen reader or large
 text, from the universal access menu (the

wiki/src/install/inc/steps/create_persistence.inline.mdwn

@@ -107,7 +107,7 @@ Restart and activate the persistent storage
 
 1. In <span class="application">Tails Greeter</span>:
 
-   [[!img install/inc/screenshots/greeter_with_persistence.png class="screenshot" link="no" alt="Tails Greeter: 'Welcome to Tails', 'Use persistence? [Yes/No]', 'More options? [Yes/No]'" ]]
+   [[!img install/inc/screenshots/greeter_with_persistence.png class="screenshot" link="no" alt="Tails Greeter: 'Welcome to Tails!'"]]
 
    - Select your language and keyboard layout in the
      <span class="guilabel">Language & Region</span> section.

wiki/src/install/inc/steps/restart_first_time.inline.mdwn

@@ -202,7 +202,7 @@ from a Tails DVD in a similar way.</p>
 
    """]]
 
-   [[!img doc/first_steps/startup_options/tails-greeter-welcome-to-tails.png class="screenshot" link="no" alt="Tails Greeter: 'Welcome to Tails', 'More options? [Yes/No]'"]]
+   [[!img doc/first_steps/startup_options/tails-greeter-welcome-to-tails.png class="screenshot" link="no" alt="Tails Greeter: 'Welcome to Tails!'"]]
 
 1. In <span class="application">Tails Greeter</span>, select your language and
 keyboard layout in the <span class="guilabel">Language & Region</span> section.