Update changes

Changes-v3.md

@@ -32,8 +32,13 @@ These are changes that are incompatible with the v2.x.x version.
 * Validation used to work for `iat`, `nbf`, `exp` fields where these fields were
   set to the explicit time.Time{} zero value, but now the _presence_ of these fields matter.
 
-* `jwt.ErrInvalidJWT` has been renamed to `jwt.UnknownPayloadTypeError` to better reflect
-  what the error means
+* Error names have been renamed. For example `jwt.ErrInvalidJWT` has been renamed to
+  `jwt.UnknownPayloadTypeError` to better reflect what the error means. For other errors,
+  `func ErrXXXX()` have generally been renamed to `func XXXError()`
+
+* Validation errors are now wrapped. While `Validate()` returns a `ValidateError()` type,
+  it can also be matched against more specific error types such as `TokenExpierdError()`
+  using `errors.Is`
 
 ## JWS