Fix typo (#99)

Author: ziming

README.md

@@ -42,7 +42,7 @@ TWILIO_USERNAME=XYZ # optional when using auth token
 TWILIO_PASSWORD=ZYX # optional when using auth token
 TWILIO_AUTH_TOKEN=ABCD # optional when using username and password
 TWILIO_ACCOUNT_SID=1234 # always required
-TWILIO_FROM=100000000 # otional default from
+TWILIO_FROM=100000000 # optional default from
 TWILIO_ALPHA_SENDER=HELLO # optional
 TWILIO_DEBUG_TO=23423423423 # Set a number that call calls/messages should be routed to for debugging
 ```