add upgrading guide

Author: seanmonstar

_data/stable.yml

@@ -3,6 +3,7 @@
   guides:
   - server
   - client
+  - upgrading
 
 - title: Server
   path: "/server"
@@ -17,3 +18,7 @@
   - basic
   - advanced
   - configuration
+
+- title: Upgrading
+  path: "/upgrading"
+  guides: []

_stable/upgrading.md

@@ -0,0 +1,68 @@
+---
+title:  Upgrade from 0.14 to 1
+layout: guide
+permalink: /guides/1/upgrading/
+---
+
+This guide is meant to help you upgrade from v0.14 of hyper to v1.
+
+## Backports and Deprecations
+
+Before upgrading, you can start preparing your 0.14 code base by enabling the
+`backports` and `deprecated` features of hyper in your `Cargo.toml`. Like
+this:
+
+```toml
+[dependencies]
+hyper = { version = "0.14", features = ["etc", "backports", "deprecated"] }
+```
+
+The `backports` feature brings several of the new types from 1.0 to 0.14. If
+you enable `deprecated` feature as well, it will add deprecation warnings to
+any of hyper's types that have direct backports available.
+
+**NOTE**: This won't give you warnings about changes where backports were not
+able to be provided.
+
+## Changelog
+
+As a general rule, we tried hard to mark every possible breaking change in the
+[changelog][]. Read through the "breaking changes" section of the 1.0 releases
+(including the RC 1-4), which will provide suggestions on how to overcome each
+one.
+
+## `hyper::Body`
+
+The `Body` type has changed to be a trait (what used to be `HttpBody`).
+
+The 0.14 `Body` could be multiple variants, and in v1 they have been split into
+[distinct types][http-body-util]. You'll benefit from analzying each place you
+use `hyper::Body` to decide which solution to switch to.
+
+- In general, if you don't need a specific variant, consider making your usage
+  generic, accepting an `impl Body` (or `where B: Body`).
+- If you want a type that can be any variant, you could use `BoxBody`.
+- Otherwise, the [more specific variants][http-body-util] allow for a more
+  explicit API in your code.
+
+## `hyper::Client`
+
+The higher-level pooling `Client` was removed from hyper 1.0. A similar type
+was added to [`hyper-util`][], called [`client::legacy::Client`][legacy]. It's
+mostly a drop-in replacement.
+
+## `hyper::Server`
+
+The v0.14 `hyper::Server` does not have a drop-in replacement, since it had
+problems.
+
+For a server type that can handle both HTTP/1 and HTTP/2 at the same time,
+use the [`server::conn::auto::Builder`][auto] from [`hyper-util`][].
+
+The listening server acceptor can be replaced with a simple loop.
+
+
+[changelog]: https://github.com/hyperium/hyper/blob/master/CHANGELOG.md#v100-2023-11-15
+[`hyper-util`]: https://crates.io/crates/hyper-util
+[legacy]: https://docs.rs/hyper-util/latest/hyper_util/client/legacy/struct.Client.html
+[auto]: https://docs.rs/hyper-util/latest/hyper_util/server/conn/auto/struct.Builder.html