docs: add description about our code structure

Document most important directories when trying to understand our
project.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

CONTRIBUTING.md

@@ -117,6 +117,10 @@ Pull requests that change the vendor/ directory directly will not be accepted.
 Instead, changes should be submitted to the original package (defined by the path in `vendor/`; for example, `vendor/github.com/containers/storage` is the [containers/storage library](https://github.com/containers/storage/).
 Once the changes have been merged into the original package, Podman's vendor directory can be updated by using `go get` on the appropriate version of the package, then running `make vendor` or `make vendor-in-container`.
 
+## Codebase structure
+
+Description about important directories in our repository is found [here](./docs/CODE_STRUCTURE.md).
+
 ## Testing
 
 Podman provides an extensive suite of regression tests in the `test/` directory.

docs/CODE_STRUCTURE.md

@@ -0,0 +1,89 @@
+# Podman Codebase structure
+
+Description about important directories in our repository.
+
+### bin/
+
+- Build binaries are put here, podman, podman-remote, quadlet, etc...
+
+### cmd/
+
+ - Each directory here builds its own binary.
+
+#### cmd/podman/
+
+- Podman CLI code, CLI commands and flags are defined here, we are using the [Cobra CLI library](https://github.com/spf13/cobra) for command line parsing.
+
+#### cmd/quadlet/
+
+- Quadlet CLI code.
+
+### contrib/
+
+- CI scripts, packaging files some container image build files.
+
+### docs/
+
+- Sphinx based documentation for Podman that is build on [Read the Docs](https://readthedocs.com/) and hosted at [docs.podman.io](https://docs.podman.io/).
+- More information is found in [README.md](./README.md).
+
+### libpod/ (only works on linux and freebsd)
+- Underlying core for most Podman operations, defines container, pod, volume management operations.
+- Contains the database to store these information on disk, either Sqlite or Botldb (our old db format).
+- Integrates with our other libraries such as:
+	- containers/storage to create and mount container storage.
+	- containers/buildah for building images.
+	- containers/common/libnetwork for network management.
+
+### pkg/
+
+- Various packages to do all sorts of different things.
+
+#### pkg/api/
+
+- The HTTP REST API server code.
+
+#### pkg/bindings/
+
+- The HTTP REST API client code.
+- This package must have a stable API as it is for use by external consumers as well.
+
+#### pkg/domain/
+
+- "glue" code between cli and the actual operations performed.
+
+##### pkg/domain/entities/
+
+- The package defines two interfaces (ContainerEngine, ImageEngine) that more or less have a function for each cli command defined.
+- It also defines a lot of types (structs) for the various options the functions accept.
+
+##### pkg/domain/infra/tunnel/
+
+- Implements the two interfaces for the remote mode (podman-remote) which just maps each operations to the bindings code from pkg/bindings which then talks to the remote server.
+
+##### pkg/domain/infra/abi/
+
+- Implements the two interfaces for the local mode (podman) that calls then directly into the core parts of libpod/ or our other libraries containers/{common,image,storage}...
+
+#### pkg/libartifact/
+
+- Core code for the new podman artifact commands.
+
+#### pkg/machine/
+
+- Core code for podman machine commands.
+
+##### pkg/machine/e2e/
+
+- e2e tests for podman machine commands.
+- Runs on Windows, MacOS and Linux.
+
+### test/
+
+- Various tests suites, see the test [README.md](../test/README.md) for more details.
+- These run on linux only.
+
+### vendor/
+
+- Directory created with "go mod vendor".
+- This includes all go deps in our repo, DO NOT edit this directory directly, changes in dependencies must be made in their respective upstream repositories and then updated in go.mod.