docs: Add WASM pages. (#1291)

* Add new wasm guide.

* Add ext docs.

* Add config section.

* Update proto.

* Update completions.

website/docs/commands/completions.mdx

@@ -2,14 +2,69 @@
 title: completions
 ---
 
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
 The `moon completions` command will generate moon command and argument completions for your current
 shell. This command will write to stdout, which can then be redirected to a file of your choice.
 
 ```shell
-$ moon completions > ~/.bash_completion.d/moon.sh
+$ moon completions > ./path/to/write/to
 ```
 
 ### Options
 
 - `--shell` - Shell to explicitly generate for. Accepts "bash", "elvish", "fish", "powershell", or
   "zsh".
+
+### Examples
+
+<Tabs
+  groupId="comp"
+  defaultValue="bash"
+  values={[
+    { label: 'Bash', value: 'bash' },
+    { label: 'Fish', value: 'fish' },
+    { label: 'Zsh', value: 'zsh' },
+  ]}
+>
+<TabItem value="bash">
+
+If using [bash-completion](https://github.com/scop/bash-completion).
+
+```shell
+$ moon completions > ~/.bash_completion.d/moon.sh
+```
+
+Otherwise write the file to a common location, and source it in your profile.
+
+```shell
+$ moon completions > ~/.bash_completions/moon.sh
+
+# In your profile
+source ~/.bash_completions/moon.sh
+```
+
+</TabItem>
+<TabItem value="fish">
+
+Write the file to Fish's completions directory.
+
+```shell
+$ moon completions > ~/.config/fish/completions/moon.fish
+```
+
+</TabItem>
+<TabItem value="zsh">
+
+If using [oh-my-zsh](https://ohmyz.sh/) (the `_` prefix is required),
+
+```shell
+$ moon completions > ~/.oh-my-zsh/completions/_moon
+
+# Reload shell (or restart terminal)
+$ omz reload
+```
+
+</TabItem>
+</Tabs>

website/docs/config/workspace.mdx

@@ -234,7 +234,8 @@ experiments:
 
 A mapping of extensions that can be downloaded and executed with the [`moon ext`](../commands/ext)
 command. An extension is a WASM plugin, and the location of the WASM file must be defined with the
-`plugin` field, which supports a relative file path or a secure URL.
+`plugin` field, which requires a
+[plugin locator string](../guides/wasm-plugins#configuring-plugin-locations).
 
 ```yaml title=".moon/workspace.yml" {2-5}
 extensions:

website/docs/guides/extensions.mdx

@@ -67,7 +67,113 @@ $ moon ext download --\
 
 ## Creating an extension
 
-Coming soon! If you're eager to get started, take a look at our [extensions repository][repo] for
-examples.
+Refer to our [official WASM guide](./wasm-plugins) for more information on how our WASM plugins
+work, critical concepts to know, how to create a plugin, and more. Once you have a good
+understanding, you may continue this specific guide.
+
+:::note
+
+Refer to our [moonrepo/moon-extensions][repo] repository for in-depth examples.
+
+:::
+
+### Implementing execution
+
+Extensions support a single plugin function, `execute_extension`, which is called by the
+[`moon ext`](../commands/ext) command to execute the extension. This is where all your business
+logic will reside.
+
+```rust
+use extism_pdk::*;
+use moon_pdk::{*, extension::*};
+
+#[host_fn]
+extern "ExtismHost" {
+    fn host_log(input: Json<HostLogInput>);
+}
+
+#[plugin_fn]
+pub fn execute_extension(Json(input): Json<ExecuteExtensionInput>) -> FnResult<()> {
+  host_log!(stdout, "Executing extension!");
+
+  Ok(())
+}
+```
+
+### Supporting arguments
+
+Most extensions will require arguments, as it provides a mechanism for users to pass information
+into the WASM runtime. To parse arguments, we provide the
+[`Args`](https://docs.rs/clap/latest/clap/trait.Args.html) trait/macro from the
+[clap](https://crates.io/crates/clap) crate. Refer to their
+[official documentation on usage](https://docs.rs/clap/latest/clap/_derive/index.html) (we don't
+support everything).
+
+```rust
+use moon_pdk::args::*;
+
+#[derive(Args)]
+pub struct ExampleExtensionArgs {
+  // --url, -u
+  #[arg(long, short = 'u', required = true)]
+  pub url: String,
+}
+```
+
+Once your struct has been defined, you can parse the provided input arguments using the
+[`parse_args`](https://docs.rs/moon_pdk/latest/moon_pdk/args/fn.parse_args.html) function.
+
+```rust
+#[plugin_fn]
+pub fn execute_extension(Json(input): Json<ExecuteExtensionInput>) -> FnResult<()> {
+  let args = parse_args::<ExampleExtensionArgs>(&input.args)?;
+
+  args.url; // --url
+
+  Ok(())
+}
+```
+
+### Supporting configuration
+
+Users can configure [extensions](../config/workspace#extensions) with additional settings in
+[`.moon/workspace.yml`](../config/workspace). Do note that settings should be in camelCase for them
+to be parsed correctly!
+
+```yaml title=".moon/workspace.yml"
+extensions:
+  example:
+    plugin: 'source:./path/to/example.wasm'
+    someSetting: 'abc'
+    anotherSetting: 123
+```
+
+In the plugin, we can map these settings (excluding `plugin`) into a struct. The `Default` trait
+must be implemented to handle situations where settings were not configured, or some are missing.
+
+```rust
+config_struct!(
+  #[derive(Default)]
+  pub struct ExampleExtensionConfig {
+    pub some_setting: String,
+    pub another_setting: u32,
+  }
+);
+```
+
+Once your struct has been defined, you can access the configuration using the
+[`get_extension_config`](https://docs.rs/moon_pdk/latest/moon_pdk/extension/fn.get_extension_config.html)
+function
+
+```rust
+#[plugin_fn]
+pub fn execute_extension(Json(input): Json<ExecuteExtensionInput>) -> FnResult<()> {
+  let config = get_extension_config::<ExampleExtensionConfig>()?;
+
+  config.another_setting; // 123
+
+  Ok(())
+}
+```
 
 [repo]: https://github.com/moonrepo/moon-extensions