docs: some minor doc-comments in client::builder

src/client/builder.rs

@@ -1,3 +1,5 @@
+//! Builder for Client
+
 use std::sync::Arc;
 
 use crate::{
@@ -12,6 +14,7 @@ use tokio_rustls::rustls::{
     SupportedProtocolVersion,
 };
 
+/// Builder for creating configured [`Client`] instance
 pub struct ClientBuilder {
     root_certs: rustls::RootCertStore,
     ss_verifier: Option<Box<dyn SelfsignedCertVerifier>>,