Add why aiscript to nav bar

Author: Folyd

docs/_meta.json

@@ -13,5 +13,10 @@
       "text": "Std Library",
       "link": "/std/overview",
       "activeMatch": "/std/"
+    },
+    {
+      "text": "Why AIScript",
+      "link": "/guide/getting-started/why-aiscript",
+      "activeMatch": "/guide/getting-started/why-aiscript"
     }
 ]

docs/guide/language/basic.mdx

@@ -351,3 +351,12 @@ for let i = 0; i < 10; i += 1 {
 // 7
 // i == 9
 ```
+
+## Environment
+
+AIScript provide a convenient way to access environment variables, the syntax is `$ENV_NAME`. You can also use [std.env](/std/env) module too.
+
+```rust
+let home = $HOME;
+print(home);
+```

docs/guide/language/class-object.md

@@ -146,7 +146,7 @@ let developer = Employee("Carlos", 28, "Software Developer");
 developer.greet(); // "Hello, my name is Carlos and I'm 28 years old, a Software Developer"
 ```
 
-:::danger
+:::danger Notice
 AIScript only support inherit single super class.
 :::
 

docs/guide/language/closure-lambda.md

@@ -179,7 +179,7 @@ fetch_data(
 );
 ```
 
-:::danger
+:::danger Notice
 AIScript current doesn't support `fn` as type annotation.
 ```rs
 fn fetch_data(url: str, on_success: fn(data: str), on_error: fn(error: str)) {}