Add contributor guidelines for where to put source code in packages

Signed-off-by: Derek McGowan <derek@mcg.dev>

CONTRIBUTING.md

@@ -83,6 +83,39 @@ contributions, see [the advanced contribution
 section](https://docs.docker.com/opensource/workflow/advanced-contributing/) in
 the contributors guide.
 
+### Where to put your changes
+
+You can make changes to any Go package within Moby outside of the vendor directory. There are no
+restrictions on packages but a few guidelines to follow for deciding on making these changes.
+When adding new packages, first consider putting them in an internal directory to prevent
+unintended importing from other modules. Code changes should either go under `api`, `client`,
+or `daemon` modules, or one of the integration test directories.
+
+Try to put a new package under the appropriate directories. The root directory is reserved for
+configuration and build files, no source files will be accepted in the root.
+
+- `api` - All types shared by client and daemon along with swagger definitions.
+- `client` - All Go files for the docker client
+- `contrib` - Files, configurations, and packages related to external tools or libraries
+- `daemon` - All Go files and packages for building the daemon
+- `docs` - All Moby technical documentation using markdown
+- `hack` - All scripts used for testing, development, and CI
+- `integration` - Testing the integration of the API, client, and daemon
+- `integration-cli` - Deprecated integration tests of the docker cli with the daemon, no new tests allowed
+- `pkg` - Legacy Go packages used externally, no new packages should be added here
+- `project` - All files related to Moby project governance
+- `vendor` - Autogenerated vendor files from `make vendor` command, do not manually edit files here
+
+The daemon module has many subpackages. Consider putting new packages under one of these
+directories.
+
+- `daemon/cmd` - All Go main packages and the packages used only for that main package
+- `daemon/internal` - All utility packages used by daemon and not intended for external use
+- `daemon/man`- All Moby reference manuals used for the `man` command
+- `daemon/plugins` - All included daemon plugins which are intended to be registered via init
+- `daemon/pkg` - All libraries used by daemon and for integration testing
+- `daemon/version` - Version package with the current daemon version
+
 ### Connect with other Moby Project contributors
 
 <table class="tg">