add infos

PotentialFlow/infos.xml

+<?xml version="1.0" encoding="utf-8"?>
+
+<models>
+	<model>
+		<title>Potential flow</title>
+		<summary>Lift and Magnus effect in 2D irrotational fluid flow</summary>
+		<file type="pro">magnus.pro</file>
+		<preview type="png">infos.png</preview>
+		<url>https://gitlab.onelab.info/doc/tutorials/wikis/Potential-flow</url>
+	</model>
+</models>