Add call-to developers on getting started page

app/assets/javascripts/components/features/getting_started/index.jsx

@@ -38,6 +38,7 @@ const GettingStarted = ({ intl, me }) => {
           <p><FormattedMessage id='getting_started.about_addressing' defaultMessage='You can follow people if you know their username and the domain they are on by entering an e-mail-esque address into the form at the top of the sidebar.' /></p>
           <p><FormattedMessage id='getting_started.about_shortcuts' defaultMessage='If the target user is on the same domain as you, just the username will work. The same rule applies to mentioning people in statuses.' /></p>
           <p><FormattedMessage id='getting_started.about_developer' defaultMessage='The developer of this project can be followed as Gargron@mastodon.social' /></p>
+          <p><FormattedMessage id='getting_started.open_source_notice' defaultMessage='Mastodon is open source software. You can contribute or report issues on github at {github}' values={{ github: <a style={{ color: '#616b86'}} href="https://github.com/tootsuite/mastodon">tootsuite/mastodon</a> }} /></p>
         </div>
       </div>
     </Column>

app/assets/javascripts/components/locales/en.jsx

@@ -27,6 +27,7 @@ const en = {
   "getting_started.about_addressing": "You can follow people if you know their username and the domain they are on by entering an e-mail-esque address into the search form.",
   "getting_started.about_shortcuts": "If the target user is on the same domain as you, just the username will work. The same rule applies to mentioning people in statuses.",
   "getting_started.about_developer": "The developer of this project can be followed as Gargron@mastodon.social",
+  "getting_started.open_source_notice": "Mastodon is open source software. You can contribute or report issues on github at {github}.",
   "column.home": "Home",
   "column.mentions": "Mentions",
   "column.public": "Public",