Update readme to clarify secret key sentence

Instead of using the verb "encrypt", it now uses the verb "sign". This
difference is significant because the values stored in the cookie are
inspectable by the user, but not modifiable. Saying it is encrypted
might lead people to think that it's not inspectable.

README.md

@@ -23,11 +23,11 @@ import {
 
 ### Setup secret key
 
-Fresh Session currently use [JSON Web Token](https://jwt.io/) under the hood to
+Fresh Session currently uses [JSON Web Token](https://jwt.io/) under the hood to
 create and manage session in the cookies.
 
-JWT requires to have a secret key to encrypt new token. Fresh Session use the
-session from your [environment variable](https://deno.land/std/dotenv/load.ts)
+JWT requires a secret key to sign new tokens. Fresh Session uses the
+secret key from your [environment variable](https://deno.land/std/dotenv/load.ts)
 `APP_KEY`.
 
 If you don't know how to setup environment variable locally, I wrote