Copy docs/appcast.xml file from main branch and move to root

appcast.xml

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+<?xml version="1.0" standalone="yes"?>
+<rss xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" version="2.0">
+    <channel>
+        <title>Transfer Toolbox</title>
+        <item>
+            <title>1.1.0</title>
+            <sparkle:releaseNotesLink>https://transfertoolbox.io/appcast.html</sparkle:releaseNotesLink>
+            <pubDate>Sun, 03 Dec 2023 15:00:52 +1100</pubDate>
+            <sparkle:version>4</sparkle:version>
+            <sparkle:shortVersionString>1.1.0</sparkle:shortVersionString>
+            <sparkle:minimumSystemVersion>12.6</sparkle:minimumSystemVersion>
+            <enclosure url="https://github.com/latenitefilms/TransferToolbox/releases/download/1.1.0/Transfer-Toolbox-1-1-0.zip" length="3958610" type="application/octet-stream" sparkle:edSignature="tVlH0ugDqrLTOwcD/xYnEpokyKD9lz120PtuvLC7BCrLc4LAEpPNzskrLG+3CvqETXY+a00Tvor/0vfSHqbcCg=="/>
+        </item>
+        <item>
+            <title>1.0.2</title>
+            <sparkle:releaseNotesLink>https://transfertoolbox.io/appcast.html</sparkle:releaseNotesLink>
+            <pubDate>Sun, 18 Jun 2023 09:49:47 +1000</pubDate>
+            <sparkle:version>3</sparkle:version>
+            <sparkle:shortVersionString>1.0.2</sparkle:shortVersionString>
+            <sparkle:minimumSystemVersion>12.6</sparkle:minimumSystemVersion>
+            <enclosure url="https://github.com/latenitefilms/TransferToolbox/releases/download/1.0.2/Transfer-Toolbox-1-0-2.zip" length="3935649" type="application/octet-stream" sparkle:edSignature="jSTaLZeZO05Z+po3vYucUyeDGiMos64rpuSssJir7W4IqRdrw5iENR0yc+3VsXztWsQhxirfoeGwrC46eylRAg=="/>
+        </item>
+    </channel>
+</rss>