Added section introducing WAT

Author: catamorphism

component-model/examples/tutorial/wat/adder/add.wat

@@ -3,5 +3,5 @@
        local.get $lhs
        local.get $rhs
        i32.add)
-    (export "docs:adder/add@0.1.0#add" (func $add))
+   (export "docs:adder/add@0.1.0#add" (func $add))
 )

component-model/src/language-support.md

@@ -21,7 +21,8 @@ Each section covers how to build and
 run components for a given toolchain:
 
   - [Language Agnostic Tooling](./language-support/language-agnostic.md)
-    - [Building a Component with `wasm-tools`](./language-support/language-agnostic.md#building-a-component-with-wasm-tools)
+    - [WAT (WebAssembly Text Format)](./language-support/language-agnostic.md#wat-webassembly-text-format)
+    - [Building a Component from WAT with `wasm-tools`](./language-support/language-agnostic.md#building-a-component-with-wasm-tools)
     - [Running a Component with Wasmtime](./language-support/language-agnostic.md#running-a-component-with-wasmtime)
   - [C/C++ Tooling](./language-support/c.md)
     - [Building a Component with `wit-bindgen` and `wasm-tools`](./language-support/c.md#building-a-component-with-wit-bindgen-and-wasm-tools)

component-model/src/language-support/language-agnostic.md

@@ -1,10 +1,57 @@
 ## Language Agnostic Tooling
 
-### Building a Component from WebAssembly Text Format (WAT) with `wasm-tools`
-
 [`wasm-tools`](https://github.com/bytecodealliance/wasm-tools) provides a suite of subcommands for
 working with WebAssembly modules and components.
 
+### WAT (WebAssembly Text Format)
+
+WAT (WebAssembly Text Format) is a text-based language
+that can be compiled to the WebAssembly binary format
+by `wasm-tools` and other tools.
+It's useful for writing small examples for testing and experimentation.
+
+Here's an example of a module expressed in WAT:
+```wat
+{{#include ../../examples/tutorial/wat/adder/add.wat}}
+```
+
+The module contains two top-level declarations, a function and an export.
+
+The function declaration declares a function named `$add`
+with two arguments, `$lhs` and `$rhs`.
+(Variable names in WAT always start with a `$`.)
+Argument and result types need to be provided explicitly.
+In this case, the types of both arguments and the result
+are `i32` (32-bit integer).
+The body of the function is a list of WebAssembly instructions.
+The two `local.get` instructions push the values of `$lhs` and `$rhs`
+onto the stack.
+The `i32.add` instruction pops the two top values off the stack
+and adds them, leaving the result on the stack.
+
+The `export` declaration connects the function that was just declared
+to a name that should be used for calling it externally.
+We want to use this WAT code to implement the interface specified in a WIT file,
+so the external name has to follow a certain convention.
+The name `"docs:adder/add@0.1.0#add"` can be broken down as follows:
+* `docs` is the package name.
+* `adder` is the name of a world inside the `docs` package.
+* `add` is the name of an interface defined in that world.
+* 0.1.0 is a version number.
+* Separately, `add` is the name of a function defined in the `add` interface.
+All of these pieces come from the specific `.wit` file we are using
+(see below).
+
+There's much more than WAT can do;
+see the Mozilla Developer Network's [a detailed guide to WAT](https://developer.mozilla.org/en-US/docs/WebAssembly/Guides/Understanding_the_text_format)
+for more information.
+
+The [wat2wasm](https://github.com/WebAssembly/wabt) tool converts
+from WAT to the binary `.wasm` format,
+but it does not create components.
+
+### Building a Component from WAT with `wasm-tools`
+
 `wasm-tools` can be used to create a component from WAT.
 Here's how to create a component from WAT
 that implements the [`adder` world](https://github.com/bytecodealliance/component-docs/blob/main/component-model/examples/tutorial/wit/adder/world.wit)
@@ -21,11 +68,12 @@ and simply adds two numbers.
   ```
 
 3. Define an `add` core module in WAT that exports an `add` function that adds two parameters.
-   Create a file called `add.wat` whose contents are as follows:
+   Create a file called `add.wat` whose contents are as follows
+   (the same as the example in the WAT section):
 
-  ```wat
-  {{#include ../../examples/tutorial/wat/adder/add.wat}}
-  ```
+```wat
+{{#include ../../examples/tutorial/wat/adder/add.wat}}
+```
 
 4. Use `wasm-tools` to create a binary core module with component metadata embedded inside it: