docs: typos in docs.yml (#1149)

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> [!IMPORTANT]
> Corrects a typo and adds slugs for better navigation in `docs.yml`.
> 
>   - **Typos**:
> - Corrected typo in page title from "Enviornment Variables" to
"Environment Variables" in `docs.yml`.
>   - **Slugs**:
>     - Added `slug: alias` for "@alias / @@alias" page in `docs.yml`.
> - Added `slug: description` for "@description / @@description" page in
`docs.yml`.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for 7f7cada. It will automatically
update as commits are pushed.</sup>

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fern/docs.yml

@@ -325,7 +325,7 @@ navigation:
             contents:
               - page: comments
                 path: 03-reference/baml/comments.mdx
-              - page: Enviornment Variables
+              - page: Environment Variables
                 path: 03-reference/baml/env-vars.mdx
               - page: string
                 path: 03-reference/baml/string.mdx
@@ -358,8 +358,10 @@ navigation:
           - page: What are attributes?
             path: 03-reference/baml/attributes/attributes-overview.mdx
           - page: "@alias / @@alias"
+            slug: alias
             path: 03-reference/baml/attributes/alias.mdx
           - page: "@description / @@description"
+            slug: description
             path: 03-reference/baml/attributes/description.mdx
           - page: "@skip"
             path: 03-reference/baml/attributes/skip.mdx