extend docs w/ further information

Author: felixheck

README.md

@@ -127,14 +127,14 @@ Required. Example: `https://localhost:8080/auth/realms/testme`<br/>
 Required. Example: `foobar`<br/>
 
 - `secret {string}` The related secret of the Keycloak client/application.<br/>
-Defining this option enables the traditional method described in the OAuth2 specification.<br/>
+Defining this option enables the traditional method described in the OAuth2 specification. To perform an almost offline validation enable the cache — a simple offline verfication with symmetric keys is not provided for security reasons.<br/>
 Optional. Example: `1234-bar-4321-foo`<br/>
 
 - `publicKey {string}` The related public key of the Keycloak client/application.<br/>
 Defining this option enables the offline validation using signed JWTs. The public key has to be in [PEM][pem] or [JWK][jwk] format. If you define neither `secret` nor `public` key, the plugin assumes that a signed JWT has to be validated – it retrieves the public key itself from `{realmUrl}/protocol/openid-connect/certs`. The offline strategy its performance is higher but the online strategy is the most flexible one.<br/>
 Optional. 
 
-- `minTimeBetweenJwksRequests {number}` – The minimum time between JWK requests in seconds.<br/>
+- `minTimeBetweenJwksRequests {number}` – The minimum time between JWKS requests in seconds.<br/>
 The value have to be a positive integer.<br/>
 Optional. Default: `0`.