Add CA certificates to NUTS node truststore instructions

Updated NUTS_README.md to include steps for adding CA and Test CA certificates to the `tls.truststorefile` of the NUTS node. This ensures proper validation of server certificates during the setup process.

NUTS_README.md

@@ -6,6 +6,8 @@ The following is required to load the VC into the NUTS node
  * A UZI Server Certificate and private key, either a test or production. In order to use the test certificate, the `-t` option must be provided.
  * This tool, make sure to run `make build` for generating the binary. For more details see the [README.md](README.md) file.
  * A running NUTS node to create a did and load the certificate. The NUTS node will be referred to as ``${nuts_base_url}``
+ * The NUTS node should have the [CA](http://cert.pkioverheid.nl/PrivateRootCA-G1.cer) cert added to the ca certificate chain `tls.truststorefile`.
+ * The same goes for the test certificate, the [Test CA](http://www.uzi-register-test.nl/cacerts/test_zorg_csp_private_root_ca_g1.cer) should be added to the ca certificate chain `tls.truststorefile`.
 
 ## Issuing a VC to a NUTS node.
 ### Creating the subject (only once)