minor fixes (#477)

* docs: release 2.17.0

* add `@meta` and `@@meta` docs

* update

* minor fixes

Author: ymc9

docs/reference/zmodel-language.md

@@ -955,7 +955,7 @@ model User {
 ##### @@meta
 
 ```zmodel
-attribute @meta(_ name: String, _ value: Any)
+attribute @@meta(_ name: String, _ value: Any)
 ```
 
 Adds arbitrary metadata to a model. The metadata can be accessed by custom plugins for code generation, or at runtime from the `modelMeta` object exported from `@zenstackhq/runtime/model-meta`. The `value` parameter can be an arbitrary literal expression, including object literals.