Add a note about why kitty terminfo does not have E3

See #6255

kitty/terminfo.py

@@ -111,6 +111,10 @@ string_capabilities = {
     'civis': r'\E[?25l',
     # Clear screen
     'clear': r'\E[H\E[2J',
+    # Clear scrollback. This is disabled because the clear program on Linux by default, without
+    # an option, uses it and nukes the scrollback. What's more this behavior was silently changed
+    # around 2010? Given clear is maintained as part of ncurses this kind of crap is no surprise.
+    # 'E3': r'\E[3J',
     # Make cursor appear normal
     'cnorm': r'\E[?12h\E[?25h',
     # Carriage return