docs: add a jwt example to vlib/crypto/README.md (#14872)

vlib/crypto/README.md

@@ -15,6 +15,7 @@ The implementations here are loosely based on [Go's crypto package](https://pkg.
 
 ## Examples:
 
+### AES:
 ```v
 import crypto.aes
 import crypto.rand
@@ -43,3 +44,40 @@ fn main() {
 	assert decrypted == data
 }
 ```
+
+### JWT:
+```v
+import crypto.hmac
+import crypto.sha256
+import encoding.base64
+import json
+
+struct JwtHeader {
+	alg string
+	typ string
+}
+
+struct JwtPayload {
+	sub  string
+	name string
+	iat  int
+}
+
+fn main() {
+	token := make_token()
+	println(token)
+}
+
+fn make_token() string {
+	secret := 'your-256-bit-secret'
+
+	header := base64.url_encode(json.encode(JwtHeader{'HS256', 'JWT'}).bytes())
+	payload := base64.url_encode(json.encode(JwtPayload{'1234567890', 'John Doe', 1516239022}).bytes())
+	signature := base64.url_encode(hmac.new(secret.bytes(), '${header}.$payload'.bytes(),
+		sha256.sum, sha256.block_size).bytestr().bytes())
+
+	jwt := '${header}.${payload}.$signature'
+
+	return jwt
+}
+```