updated 1.7 migration guide to call out a behavior change

website/docs/guides/migration/versions/00-upgrading-to-v1.7.md

@@ -14,11 +14,22 @@ description: New features and changes in dbt Core v1.7
 
 dbt Labs is committed to providing backward compatibility for all versions 1.x, with the exception of any changes explicitly mentioned below. If you encounter an error upon upgrading, please let us know by [opening an issue](https://github.com/dbt-labs/dbt-core/issues/new).
 
+### Behavior changes
+
+1.7 expands the amount of sources folks can configure freshness for. Previously, freshness was limited to sources that had a `loaded_at_field`; but now, freshness can be generated from warehouse metadata tables when available. 
+
+As part of this change, the `loaded_at_field` is **no longer required** in order to generate source freshness. If a source has a `freshness:` block, dbt will attempt to calculate freshness for that source:
+- if a `loaded_at_field` is provided, dbt will calculate freshness via a select query (previous behavior)
+- if a `loaded_at_field` is _not_ provided, dbt will calculate freshness via warehouse metadata tables when possible (new!)
+
+This is technically a small behavior change comapared to previous versons. In order to _not_ calculate freshness for a source:
+- don't add a `freshness:` block
+- explicity set `freshness: null`
+
 ## New and changed features and functionality
 
 - [`dbt docs generate`](/reference/commands/cmd-docs) now supports `--select` to generate documentation for a subset of your project. Currently available for Snowflake and Postgres only, but other adapters are coming soon. 
-- [Source freshness](/docs/deploy/source-freshness) can now be generated from warehouse metadata tables, currently snowflake only, but other adapters that have metadata tables are coming soon. If you configure source freshness without a `loaded_at_field`, dbt will try to determine freshness from warehouse metadata tables.
-- The nodes dictionary in the `catalog.json` can now be "partial" if `dbt docs generate` is run with a selector.
+- [Source freshness](/docs/deploy/source-freshness) can now be generated from warehouse metadata tables, currently Snowflake only, but other adapters that have metadata tables are coming soon. 
 
 ### MetricFlow enhancements
 
@@ -32,8 +43,9 @@ dbt Labs is committed to providing backward compatibility for all versions 1.x,
 
 - The [manifest](/reference/artifacts/manifest-json) schema version has been updated to v11.
 - The [run_results](/reference/artifacts/run-results-json) schema version has been updated to v5.
-- Added [node attributes](/reference/artifacts/run-results-json) related to compilation (`compiled`, `compiled_code`, `relation_name`).
-
+- There were a handful of specific changes to the [catalog.json](/reference/artifacts/catalog-json):
+    - Added [node attributes](/reference/artifacts/run-results-json) related to compilation (`compiled`, `compiled_code`, `relation_name`) to the `catalog.json`. 
+    - The nodes dictionary in the `catalog.json` can now be "partial" if `dbt docs generate` is run with a selector.
 
 ### Model governance
 
@@ -49,4 +61,4 @@ dbt Core v1.5 introduced model governance which we're continuing to refine.  v1.
 With these quick hits, you can now:
 - Configure a `delimiter` for a seed file.
 - Use packages with the same git repo and unique subdirectory.
-- Moved the `date_spine` macro from dbt-utils to dbt-core.
+- Access the `date_spine` macro directly from dbt-core (moved over from dbt-utils).