New example for methods and associated functions (FuelLabs#4226)

## Description
Closes FuelLabs#4223

Basically just showing that associated methods do actually work.

## Checklist

- [x] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

docs/book/src/basics/methods_and_associated_functions.md

@@ -7,32 +7,7 @@ _Associated functions_ are very similar to _methods_, in that they are also defi
 To declare methods and associated functions for a struct or enum, use an _impl block_. Here, `impl` stands for implementation.
 
 ```sway
-script;
-
-struct Foo {
-    bar: u64,
-    baz: bool,
-}
-
-impl Foo {
-    // this is a _method_, as it takes `self` as a parameter.
-    fn is_baz_true(self) -> bool {
-        self.baz
-    }
-
-    // this is an _associated function_, since it does not take `self` as a parameter.
-    fn new_foo(number: u64, boolean: bool) -> Foo {
-        Foo {
-            bar: number,
-            baz: boolean,
-        }
-    }
-}
-
-fn main() {
-    let foo = Foo::new_foo(42, true);
-    assert(foo.is_baz_true());
-}
+{{#include ../../../../examples/methods_and_associated_functions/src/main.sw}}
 ```
 
 To call a method, simply use dot syntax: `foo.iz_baz_true()`.

examples/Forc.lock

@@ -64,6 +64,11 @@ name = 'match_statements'
 source = 'member'
 dependencies = ['std']
 
+[[package]]
+name = 'methods_and_associated_functions'
+source = 'member'
+dependencies = ['std']
+
 [[package]]
 name = 'msg_sender'
 source = 'member'

examples/Forc.toml

@@ -4,6 +4,7 @@
 members = [
   "abi_supertraits",
   "arrays",
+  "methods_and_associated_functions",
   "asm_return_tuple_pointer",
   "break_and_continue",
   "cei_analysis",

examples/methods_and_associated_functions/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "methods_and_associated_functions"
+
+[dependencies]
+std = { path = "../../sway-lib-std" }

examples/methods_and_associated_functions/src/main.sw

@@ -0,0 +1,26 @@
+script;
+
+struct Foo {
+    bar: u64,
+    baz: bool,
+}
+
+impl Foo {
+    // this is a _method_, as it takes `self` as a parameter.
+    fn is_baz_true(self) -> bool {
+        self.baz
+    }
+
+    // this is an _associated function_, since it does not take `self` as a parameter.
+    fn new_foo(number: u64, boolean: bool) -> Foo {
+        Foo {
+            bar: number,
+            baz: boolean,
+        }
+    }
+}
+
+fn main() {
+    let foo = Foo::new_foo(42, true);
+    assert(foo.is_baz_true());
+}