add 4.0.0 disclaimer

src/gui/mainMenu/AlphaDisclaimer.tw

@@ -32,6 +32,9 @@
 	<div class="note">
 		version: $ver, mod version: $pmodVer, build: $releaseID<<if App.Version.commitHash>>, commit: <<= App.Version.commitHash>><</if>>
 	</div>
+	<span style="font-weight:Bold"> /* remove me with 4.0.0! */
+		4.0.0 is in alpha release. This means the new player content has minimal implementation.
+	</span>
 	<div id="version">
 		<<link "More version info">>
 			<<replace "#version">>