fixup! fixup! fixup! fixup! fixup! [doc] Improvements on management of trusted certificates

Signed-off-by: Ming Lu <ming.lu@cloud.com>

Author: minglumlu

doc/content/design/trusted-certificates.md

@@ -78,14 +78,13 @@ The new "pool.install_trusted_certificate" should be used instead.
 This is a new API introduced in this design with its arguments being defined as:
 * session (ref session_id): reference to a valid session;
 * self (ref Pool): reference to the pool;
-* kind (string): the kind of the certificate; it can be either "ca" or "peer";
+* ca (boolean): the trusted certificate is a root CA certificate used to verify a chain (true), or a peer certificate used for certificate pinning (false);
 * cert (string): the trusted certificate in PEM format;
 * purpose (string list): the purposes of the trusted certificate.
 
 This new API is used to install trusted certificate.
-The value of *kind* can be "ca", which stands for root CA certificate, or "peer" which stands for peer certificate.
 When *purpose* is an empty set, it stands for a root CA certificate for general purpose.
-The *purpose* can not be an empty set when the *kind* is "peer", because each peer certificate is specific to a single server and therefore unsuitable for a shared trusted certificate for general purpose.
+The *purpose* can not be an empty set when the *ca* is false, because each peer certificate is specific to a single server and therefore unsuitable for a shared trusted certificate for general purpose.
 
 ### pool.uninstall_certificate
 This is a new API introduced in this design to uninstall a trusted certificate with its arguments being defined as: