unannex figure .png files for proper readme

.gitattributes

@@ -1,3 +1,4 @@
 * annex.backend=MD5E
 **/.git* annex.largefiles=nothing
+**/figures* annex.largefiles=((largerthan=100kb) and not (include=*.png))
 * annex.largefiles=((mimeencoding=binary)and(largerthan=0))