update readme

README.md

@@ -3,7 +3,7 @@
 
 ## Legal:
 
-Copyright (2016) Tom Dwelly 
+Copyright (2016-2021) Tom Dwelly 
 
 > Speccy is free software: you can redistribute it and/or modify
 > it under the terms of the GNU General Public License as published by
@@ -30,6 +30,11 @@ of an appropriately formatted spectral file. e.g.
 
 (substitute URL of a valid speccy file)
 
+Note that modern cross-site scripting prevention measures in the
+browser generally prevent one from loading a specfile from a webserver
+that is different from the one hosting the speccy webapp.
+
+
 ## Controls:
 * The cursor (arrow) keys move the template in redshift and normalisation
 * To zoom into a region: click and hold the right mouse button at one corner