fix(migration.md): migration guide for new litellm MAJOR release

docs/my-website/docs/migration.md

@@ -3,8 +3,18 @@
 When we have breaking changes (i.e. going from 1.x.x to 2.x.x), we will document those changes here.
 
 
-🧹 nothing here yet.. 
+## `1.0.0` 
 
+**Last Release before breaking change**: 0.14.0
+
+**What changed?**
+
+- Requires `openai>=1.0.0`
+- `openai.InvalidRequestError` → `openai.BadRequestError`
+- `openai.ServiceUnavailableError` → `openai.APIStatusError`
+- *NEW* litellm client, allow users to pass api_key
+    - `litellm.Litellm(api_key="sk-123")`
+- response objects now inherit from `BaseModel` (prev. `OpenAIObject`)
 
 **How can we communicate changes better?**
 Tell us