AddonManager: add gitattributes file to let git manage file endings and normalize them

src/Mod/AddonManager/.gitattributes

@@ -0,0 +1,26 @@
+# for more information see forum topic and pull request
+# https://github.com/FreeCAD/FreeCAD/pull/2752
+# https://forum.freecadweb.org/viewtopic.php?f=17&t=41117
+
+
+# get all used file types
+# in a directory in a bash use
+# find . -type f -name '*.*' | sed 's|.*\.||' | sort -u
+# add all of them either to text or binary
+
+
+# Explicitly declare which files we wish to always normalize line-endings on
+# standard endings
+*.csv text
+*.dox text
+*.py text
+*.qrc text
+*.sh text
+*.ts text
+*.txt text
+*.ui text
+*.yml text
+
+
+# use git to manually correct the file endings
+# git add --renormalize .