update update doc

docs/UPDATING.md

@@ -5,7 +5,19 @@ as follows:
 
 - Bump submodules
   - `./duckdb` should be set to latest tagged release
-  - `./extension-ci-tools` should be set to updated branch corresponding to latest DuckDB release
+  - `./extension-ci-tools` should be set to updated branch corresponding to latest DuckDB release. So if you're building for DuckDB `v1.1.0` there will be a branch in `extension-ci-tools` named `v1.1.0` to which you should check out. 
 - Bump versions in `./github/workflows`
-  - `duckdb_version` input in `MainDistributionPipeline.yml` should be set to latest tagged release
+  - `duckdb_version` input in `duckdb-stable-build` job in `MainDistributionPipeline.yml` should be set to latest tagged release
+  - `duckdb_version` input in `duckdb-stable-deploy` job in `MainDistributionPipeline.yml` should be set to latest tagged release
+  - the reusable workflow `duckdb/extension-ci-tools/.github/workflows/_extension_distribution.yml` for the `duckdb-stable-build` job should be set to latest tagged release
 
+# API changes
+DuckDB extensions built with this extension template are built against the internal C++ API of DuckDB. This API is not guaranteed to be stable.
+What this means for extension development is that when updating your extensions DuckDB target version using the above steps, you may run into the fact that your extension no longer builds properly.
+
+Currently, DuckDB does not (yet) provide a specific change log for these API changes, but it is generally not too hard to figure out what has changed.
+
+For figuring out how and why the C++ API changed, we recommend using the following resources:
+- DuckDB's [Release Notes](https://github.com/duckdb/duckdb/releases)
+- DuckDB's history of [Core extension patches](https://github.com/duckdb/duckdb/commits/main/.github/patches/extensions)
+- The git history of the relevant C++ Header file of the API that has changed