Add FAQ about updating the app

Addresses #3104

Added separate answers for the Downloaded vs Play store versions. Also noted that school managed installations would have to be updated by administrators.

src/views/download/download.jsx

@@ -237,7 +237,24 @@ class Download extends React.Component {
                         <p>
                             <FormattedMessage id="download.onPhoneAnswer" />
                         </p>
-
+                        <h3 className="faq-question">
+                            <FormattedMessage id="download.howUpdateApp" />
+                        </h3>
+                        {isDownloaded(this.state.OS) && (
+                            <p>
+                                <FormattedMessage
+                                    id="download.howUpdateAppAnswerDownload"
+                                    values={{operatingsystem: this.state.OS}}
+                                />
+                            </p>
+                        )}
+                        {isFromGooglePlay(this.state.OS) && (
+                            <p>
+                                <FormattedMessage
+                                    id="download.howUpdateAppAnswerApp"
+                                />
+                            </p>
+                        )}
                         <h3 className="faq-question">
                             <FormattedMessage id="download.whenSupportLinuxApp" />
                         </h3>

src/views/download/l10n.json

@@ -36,6 +36,9 @@
   "download.yesAnswer" : "Yes.",
   "download.onPhone": "Can I install Scratch on my Android phone?",
   "download.onPhoneAnswer" : "No. The current version of Scratch for Android only works on tablets.",
+  "download.howUpdateApp" : "How do I update the Scratch app?",
+  "download.howUpdateAppAnswerApp" : "Open the Google Play store and check for updates. If your installation is managed by school administrators, they will need to update the version and make the update available to managed devices.",
+  "download.howUpdateAppAnswerDownload" : "To update Scratch for {operatingsystem} from this page, download the latest version and install. To check which version you have, click the Scratch logo.",
   "download.canIShare": "Can I share from Scratch Desktop?",
   "download.canIShareAnswer": "This isn’t supported currently. For now, you can save a project from Scratch Desktop, upload it to your Scratch account, and share it there. In a later version we will add the ability to upload to your Scratch account directly in Scratch Desktop.",
   "download.canIShareApp": "Can I share to the online community from the Scratch app for {operatingsystem}?",