feat (docs): add info around custom models to google vertex provider (#…

…3346)

Co-authored-by: 🤖Esteban Dalel R <[email protected]>

content/providers/01-ai-sdk-providers/11-google-vertex.mdx

@@ -98,8 +98,15 @@ The first argument is the model id, e.g. `gemini-1.5-pro`.
 const model = vertex('gemini-1.5-pro');
 ```
 
-Google Vertex models support also some model specific settings that are not part of the [standard call settings](/docs/ai-sdk-core/settings).
-You can pass them as an options argument:
+<Note>
+  If you are using [your own
+  models](https://cloud.google.com/vertex-ai/docs/training-overview), the name
+  of your model needs to start with `projects/`.
+</Note>
+
+Google Vertex models support also some model specific settings that are not part
+of the [standard call settings](/docs/ai-sdk-core/settings). You can pass them as
+an options argument:
 
 ```ts
 const model = vertex('gemini-1.5-pro', {