Enable display country flag instead of spelllang

doc/airline.txt

@@ -146,6 +146,9 @@ values):
   (if enough space is available) >
   let g:airline_detect_spelllang=1
 <
+  Set to 'flag' to get a unicode icon of the relavant country flag instead of
+  the 'spelllang' itself
+
 * enable iminsert detection >
   let g:airline_detect_iminsert=0
 <