docs(client,server): added note about stability of Builder struct default options (#3366)

Closes #3336

Author: newmanifold

src/client/conn/http1.rs

@@ -97,6 +97,9 @@ where
 /// A builder to configure an HTTP connection.
 ///
 /// After setting options, the builder is used to create a handshake future.
+///
+/// **Note**: The default values of options are *not considered stable*. They
+/// are subject to change at any time.
 #[derive(Clone, Debug)]
 pub struct Builder {
     h09_responses: bool,

src/client/conn/http2.rs

@@ -50,6 +50,9 @@ where
 /// A builder to configure an HTTP connection.
 ///
 /// After setting options, the builder is used to create a handshake future.
+///
+/// **Note**: The default values of options are *not considered stable*. They
+/// are subject to change at any time.
 #[derive(Clone, Debug)]
 pub struct Builder<Ex> {
     pub(super) exec: Ex,

src/server/conn/http1.rs

@@ -41,6 +41,9 @@ pin_project_lite::pin_project! {
 }
 
 /// A configuration builder for HTTP/1 server connections.
+///
+/// **Note**: The default values of options are *not considered stable*. They
+/// are subject to change at any time.
 #[derive(Clone, Debug)]
 pub struct Builder {
     timer: Time,

src/server/conn/http2.rs

@@ -35,6 +35,9 @@ pin_project! {
 }
 
 /// A configuration builder for HTTP/2 server connections.
+///
+/// **Note**: The default values of options are *not considered stable*. They
+/// are subject to change at any time.
 #[derive(Clone, Debug)]
 pub struct Builder<E> {
     exec: E,