docs: add notes about pipelining

README.md

@@ -37,7 +37,8 @@ The benchmark is a simple `hello world` [example](benchmarks/index.js) without p
 <a name='client'></a>
 ### `new undici.Client(url, opts)`
 
-A basic HTTP/1.1 client, mapped on top a single TCP/TLS connection.
+A basic HTTP/1.1 client, mapped on top a single TCP/TLS connection. Pipelining is disabled
+by default.
 
 `url` can be a string or a [`URL`](https://nodejs.org/api/url.html#url_class_url) object.
 It should only include the protocol, hostname, and the port.
@@ -71,6 +72,10 @@ Options:
 - `pipelining: Number`, the amount of concurrent requests to be sent over the
   single TCP/TLS connection according to
   [RFC7230](https://tools.ietf.org/html/rfc7230#section-6.3.2).
+  Carefully consider your workload and environment before enabling concurrent requests
+  as pipelining may instead significantly reduce performance if used incorrectly.
+  Pipelining is sensitive to network stack settings as well as head of line blocking
+  caused by long running requests.
   Default: `1`.
 
 - `tls: Object|Null`, an options object which in the case of `https` will be passed to