Improve phrasing

- Privacy is more vague than surveillance
- Be shorter
- Be more consistent with the phrasing of our mission
- Simplify syntax by removing a verb

wiki/src/index.html

@@ -18,8 +18,8 @@ document.addEventListener('DOMContentLoaded', function() {
 <h1 class="sentence">
 <span class="hero-tails">Tails</span><br/>
 is a portable operating system<br class="optional"/>
-that protects your privacy<br class="optional"/>
-and helps you avoid censorship.
+that protects against<br class="optional"/>
+surveillance and censorship.
 </h1>
 
 </div>