update changeset entry to clarify breaking changes for API surface

Author: s-sajid-ali

.changeset/default_to_httpx2.md

@@ -2,4 +2,8 @@
 default: major
 ---
 
-# Default to using httpx2
+# Default to using httpx2 instead of httpx causing the following breaking API changes:
+- `set_httpx_client` -> `set_httpx2_client`
+- `get_httpx_client` -> `get_httpx2_client`
+- `set_async_httpx_client` -> `set_async_httpx2_client`
+- `get_async_httpx_client` -> `get_async_httpx2_client`