Update rust guest example comments in README.md (#599)

* Update rust guest example comments in README.md

* Shorten the explanations on export_host macro

Co-authored-by: Kyle Brown <kylebrw@gmail.com>

---------

Co-authored-by: Kyle Brown <kylebrw@gmail.com>

README.md

@@ -9,7 +9,7 @@
     </strong>
   </p>
 
-  <strong>A <a href="https://bytecodealliance.org/">Bytecode Alliance</a> project</strong>
+<strong>A <a href="https://bytecodealliance.org/">Bytecode Alliance</a> project</strong>
 
   <p>
     <a href="https://github.com/bytecodealliance/wit-bindgen/actions?query=workflow%3ACI"><img src="https://github.com/bytecodealliance/wit-bindgen/workflows/CI/badge.svg" alt="build status" /></a>
@@ -157,9 +157,8 @@ which has a `_start` entrypoint (e.g. a `src/main.rs` in Rust).
 [non-command]: https://github.com/bytecodealliance/wasmtime/releases/latest/download/wasi_snapshot_preview1.reactor.wasm
 [command]: https://github.com/bytecodealliance/wasmtime/releases/latest/download/wasi_snapshot_preview1.command.wasm
 
-
-
 ## Supported Guest Languages
+
 [guests]: #supported-guest-languages
 
 The `wit-bindgen` project is primarily focused on **guest** languages which are
@@ -215,7 +214,7 @@ file. Example code using this then looks like:
 wit_bindgen::generate!("host");
 
 // Define a custom type and implement the generated `Host` trait for it which
-// represents implementing all the necesssary exported interfaces for this
+// represents implementing all the necessary exported interfaces for this
 // component.
 struct MyHost;
 
@@ -225,6 +224,7 @@ impl Host for MyHost {
     }
 }
 
+// The following macro is generated by wit-bindgen and is always named `export_{world_name}`
 export_host!(MyHost);
 ```
 
@@ -301,7 +301,6 @@ Like with Rust, you can then inspect the output binary:
 wasm-tools component wit ./my-component.wasm
 ```
 
-
 ### Guest: Java
 
 Java bytecode can be compiled to WebAssembly using
@@ -380,6 +379,7 @@ ideally relatively quickly follow suit and stay within the confines of the
 first design.
 
 ## CLI Installation
+
 [cli-install]: #cli-installation
 
 To install the CLI for this tool (which isn't the only way it can be used), run
@@ -394,8 +394,8 @@ This CLI **IS NOT** stable and may change, do not expect it to be or rely on it
 being stable. Please reach out to us on [zulip] if you'd like to depend on it,
 so we can figure out a better alternative for your use case.
 
-
 ## Host Runtimes for Components
+
 [hosts]: #host-runtimes-for-components
 
 The `wit-bindgen` project is intended to facilitate in generating a component,
@@ -404,31 +404,31 @@ execute that somewhere. This is not under the purview of `wit-bindgen` itself
 but these are some resources and runtimes which can help you work with
 components:
 
-* Rust: the [`wasmtime` crate](https://docs.rs/wasmtime) is an implementation of
+- Rust: the [`wasmtime` crate](https://docs.rs/wasmtime) is an implementation of
   a native component runtime that can run any WIT `world`. It additionally comes
   with a [`bindgen!`
   macro](https://docs.rs/wasmtime/latest/wasmtime/component/macro.bindgen.html)
   which acts similar to the `generate!` macro in this repository. This macro
   takes a [WIT] package as input and generates `trait`-based bindings for the
   runtime to implement and use.
 
-* JS: the [`js-component-tools`] project can be used to execute components in JS
+- JS: the [`js-component-tools`] project can be used to execute components in JS
   either on the web or outside the browser in a runtime such as `node`. This
   project generates a polyfill for a single concrete component to execute in a
   JS environment by extracting the core WebAssembly modules that make up a
   component and generating JS glue to interact between the host and these
   modules.
 
-* Python: the [`wasmtime`](https://github.com/bytecodealliance/wasmtime-py)
+- Python: the [`wasmtime`](https://github.com/bytecodealliance/wasmtime-py)
   project [on PyPI](https://pypi.org/project/wasmtime/) has a `bindgen` mode
   that works similar to the JS integration. Given a concrete component this will
   generate Python source code to interact with the component using an embedding
   of Wasmtime for its core WebAssembly support.
 
-* Tooling: the [`wasm-tools`] project can be used to inspect and modify
+- Tooling: the [`wasm-tools`] project can be used to inspect and modify
   low-level details of components. For example as previously mentioned you can
   inspect the WIT-based interface of a component with `wasm-tools component
-  wit`. You can link two components together with `wasm-tools compose` as well.
+wit`. You can link two components together with `wasm-tools compose` as well.
 
 [`js-component-tools`]: https://github.com/bytecodealliance/js-component-tools