docs(README): mention alternative method to set token

README.md

@@ -55,7 +55,7 @@ go build .
 
 1. Run the `discordo` executable with no arguments.
 
-> If you are logging in using an authentication token, provide the `token` command-line flag to the executable (eg: `--token "OTI2MDU5NTQxNDE2Nzc5ODA2.Yc2KKA.2iZ-5JxgxG-9Ub8GHzBSn-NJjNg"`). The token is stored securely in the default OS-specific keyring.
+> If you are logging in using an authentication token, provide the `token` command-line flag to the executable (eg: `--token "OTI2MDU5NTQxNDE2Nzc5ODA2.Yc2KKA.2iZ-5JxgxG-9Ub8GHzBSn-NJjNg"`). Alternatively, set the value of the `DISCORDO_TOKEN` environment variable to the authentication token. The token is stored securely in the default OS-specific keyring.
 
 2. Enter your email and password and click on the "Login" button to continue.