add selector variable (#564)

Author: rephus

self-host/customize-deployment/environment-variables.mdx

@@ -600,6 +600,7 @@ The admin, organization, and API key variables from [Initialize instance](#initi
 | `repository`            | Yes      | Repository in `org/repo` format.                               |
 | `branch`                | Yes      | Branch name to pull the dbt project from.                      |
 | `project_sub_path`      | Yes      | Subdirectory path within the repo (use `/` for the root).      |
+| `selector`              | No       | dbt [selector](https://docs.getdbt.com/reference/node-selection/yaml-selectors) name to limit which models are compiled. |
 
 ### Example