docs: document --combine-manifest flag on lightdash deploy

references/lightdash-cli.mdx

@@ -443,6 +443,8 @@ All standard [dbt options](#dbt-options) work with `lightdash deploy`.
 - `--use-dbt-list [true|false]`
   - (default: true)
   - Use `dbt list` instead of `dbt compile` to generate dbt manifest.json
+- `--combine-manifest <path>`
+  - Path to an additional dbt `manifest.json`. Models present in this file but missing from the deploy-generated manifest are merged in so the deploy reflects the full project even when dbt was only run on a subset of models. The deploy-generated manifest always wins on conflicts.
 - `--use-batched-deploy`
   - (default: false)
   - Deploy explores in batches instead of a single request. Useful for large projects that exceed payload size limits
@@ -474,6 +476,12 @@ Deploy with custom batch settings for very large projects:
 lightdash deploy --use-batched-deploy --batch-size 100 --parallel-batches 3
 ```
 
+Deploy a subset of models while keeping the rest of the project intact by merging in an existing manifest:
+
+```bash
+lightdash deploy --select "tag:marketing" --combine-manifest ./prod-manifest.json
+```
+
 
 ### `lightdash refresh`