Deprecation notice for secp256k1 curve in EC algorithm (#528)

* Deprecation notice for secp256k1 curve in EC algorithm

* Mentioned no support for secp256k1 after Java 15+

README.md

@@ -46,10 +46,11 @@ The library implements JWT Verification and Signing using the following algorith
 | RS384 | RSA384 | RSASSA-PKCS1-v1_5 with SHA-384 |
 | RS512 | RSA512 | RSASSA-PKCS1-v1_5 with SHA-512 |
 | ES256 | ECDSA256 | ECDSA with curve P-256 and SHA-256 |
-| ES256K | ECDSA256 | ECDSA with curve secp256k1 and SHA-256 |
 | ES384 | ECDSA384 | ECDSA with curve P-384 and SHA-384 |
 | ES512 | ECDSA512 | ECDSA with curve P-521 and SHA-512 |
 
+⚠️ Note - ECDSA with curve secp256k1 and SHA-256 will not be supported for Java 15+ by this library since it has been (disabled in Java 15)[https://www.oracle.com/java/technologies/javase/15-relnote-issues.html#JDK-8237219]
+
 ## Usage
 
 ### Pick the Algorithm