Update link to getting started guide (#26)

Use the new link to the getting started guide under
`docs.simpeg.xyz/latest`. The previous link redirects to the new one, so
this is not a critical change.

Author: santisoler

Diff for: index.html

@@ -180,7 +180,7 @@ <h2 id="start">&#x1F680; Get Started &#x1F680;</h2>
                 <ul class="icons">
                     <li>
                       <i class="fab fa-python fa-lg"></i>
-                      <a href="https://docs.simpeg.xyz/content/getting_started/installing.html">
+                      <a href="https://docs.simpeg.xyz/latest/content/getting_started/installing.html">
                         Install SimPEG
                       </a>
                     </li>