Updated multiple mutations info.

docs/docker.rst

@@ -144,7 +144,7 @@ Multiple point mutation calculations
 ------------------------------------
 Sometimes, we need to see effects of double or triple mutations. ESCOTT can 
 perform calculations if you provide a mut file. Double or triple mutations should be separated 
-with a colon. In this case, the mut file must
+with a colon and do not forget to add a new line after the last line of mutations. In this case, the mut file must
 have the following format:
 
 .. code:: bash