Added host and certificate chain validation sections to the README.

README.md

@@ -989,6 +989,20 @@ These server trust policies will result in the following behavior:
 * `insecure.expired-apis.com` will never evaluate the certificate chain and will always allow the TLS handshake to succeed.
 * All other hosts will use the default evaluation provided by Apple.
 
+#### Validating the Host
+
+The `.PerformDefaultEvaluation`, `.PinCertificates` and `.PinPublicKeys` server trust policies all take a `validateHost` parameter. Setting the value to `true` will cause the server trust evaluation to verify that hostname in the certificate matches the hostname of the challenge. If they do not match, evaluation will fail. A `validateHost` value of `false` will still evaluate the full certificate chain, but will not validate the hostname of the leaf certificate.
+
+> It is recommended that `validateHost` always be set to `true` in production environments.
+
+#### Validating the Certificate Chain
+
+Pinning certificates and public keys both have the option of validating the certificate chain using the `validateCertificateChain` parameter. By setting this value to `true`, the full certificate chain will be evaluated in addition to performing a byte equality check against the pinned certficates or public keys. A value of `false` will skip the certificate chain validation, but will still perform the byte equality check.
+
+There are several cases where it may make sense to disable certificate chain validation. The most common use cases for disabling validation are self-signed and expired certificates. The evaluation would always fail in both of these cases, but the byte equality check will still ensure you are receiving the certificate you expect from the server.
+
+> It is recommended that `validateCertificateChain` always be set to `true` in production environments.
+
 * * *
 
 ## FAQ