docs: fix broken example link in README (#504)

The link to the 'building and signing a token' example pointed to
#example-New-Hmac which no longer exists. Update to the correct
anchor #example-NewWithClaims-Hmac.

Fixes #501

Author: Yanhu007

README.md

@@ -98,7 +98,7 @@ for examples of usage:
 * [Simple example of parsing and validating a
   token](https://pkg.go.dev/github.com/golang-jwt/jwt/v5#example-Parse-Hmac)
 * [Simple example of building and signing a
-  token](https://pkg.go.dev/github.com/golang-jwt/jwt/v5#example-New-Hmac)
+  token](https://pkg.go.dev/github.com/golang-jwt/jwt/v5#example-NewWithClaims-Hmac)
 * [Directory of
   Examples](https://pkg.go.dev/github.com/golang-jwt/jwt/v5#pkg-examples)