Fix module env usage tip (#1423)

* Fix module env usage tip

Fixes #1024

Use a more concise example, similar to the previous one.

Add usage example with proof.

* Improve wording

The 'also' serves no purpose. It's unclear what [previous content] it refers to.

book/modules.md

@@ -265,7 +265,7 @@ As you can see, defining the submodule structure also shapes the command line AP
 
 ## Environment Variables
 
-Modules can also define an environment using [`export-env`](/commands/docs/export-env.md):
+Modules can define an environment using [`export-env`](/commands/docs/export-env.md):
 
 ```nu
 # greetings.nu
@@ -292,22 +292,28 @@ hello Arthur, King of the Britons!
 ```
 
 ::: tip
-You can put a complex code defining your environment without polluting the namespace of the module, for example:
+The module implementation can use its own scoped environment variables without them bleeding into users scope. For example:
 
 ```nu
- def tmp [] { "tmp" }
- def other [] { "other" }
+# greetings-local.nu
 
- let len = (tmp | str length)
-
- load-env {
- OTHER_ENV: (other)
- TMP_LEN: $len
- }
+export def hello [] {
+ $env.MYNAMELOCAL = "Arthur, King of the Britons"
+ $"hello ($env.MYNAMELOCAL)"
 }
 ```
 
-Only `$env.TMP_LEN` and `$env.OTHER_ENV` are preserved after evaluating the `export-env` module.
+```nu
+> use greetings-local.nu
+
+> $env.MYNAMELOCAL
+Error: nu::shell::column_not_found
+[…]
+
+> greetings-local hello
+hello Arthur, King of the Britons!
+```
+
 :::
 
 ## Caveats