Fix preposition in banner text (#25)

Author: agners

rootfs/etc/welcome.txt

@@ -5,7 +5,7 @@
 | |  | | (_) | | | | | |  __/  / ____ \\__ \__ \ \__ \ || (_| | | | | |_ 
 |_|  |_|\___/|_| |_| |_|\___| /_/    \_\___/___/_|___/\__\__,_|_| |_|\__|
 
-Welcome on Home Assistant command line.
+Welcome to the Home Assistant command line.
 
 For more details use 'help' and 'exit' to close.
 If you need access to host system use 'login'.