directory structure docs

Summary: First pass at docs. This is probably enough for PP can do deeper for MVP

Reviewed By: digantdesai, cccclai

Differential Revision: D47881211

fbshipit-source-id: a161962b0c85b8a9aaa20d2080e1e0b3603c76c6

Author: JacobSzwejbka

README.md

@@ -44,5 +44,56 @@ Compared to the legacy Lite Interpreter, there are some major benefits:
     - [Delegate to a backend](/docs/website/docs/tutorials/backend_delegate.md)
 - [Executorch Google Colab](https://colab.research.google.com/drive/1oJBt3fj_Tr3FE7L9RdUgSKK9XzJfUv4F#scrollTo=fC4CB3kFhHPJ)
 
+## Directory Structure [WIP]
+
+executorch
+├── backends                        #  1st party backend implementations.
+|   ├── xnnpack
+|   ├── vulkan
+|   ├── backend_api.py              # TODO move to exir/backend
+|   ├── backend_details.py          # TODO move to exir/backend
+|   ├── partioner.py                # TODO move to exir/backend
+├── build                           #  Utilities for managing the build system.
+├── bundled_program                 #  Utilities for attaching reference inputs and outputs to models. TODO move to extension
+├── codegen                         #  Tooling to autogenerate bindings between kernels and the runtime. TODO move to tool
+├── configurations                  #  TODO delete this
+├── docs                            #  Static docs tooling
+├── examples                        #  Examples of various user flows, such as model export and delegates.
+|   ├── export
+|   ├── models
+├── exir                            #  Ahead of time library, model capture and lowering apis.
+|   ├── capture                     #  Program capture.
+|   ├── dialects                    #  Op sets for various dialects in the export process.
+|   ├── emit                        #  Conversion from ExportedProgram to Executorch execution instructions.
+|   ├── program                     #  Export artifacts.
+|   ├── serialize                   #  Serialize final export artifact.
+├── extension                       #  Extensions built on top of the runtime.
+|   ├── aten_util
+|   ├── data_loader                 # 1st party data loader implementations.
+|   ├── memory_allocator            # 1st party memory allocator implementations.
+|   ├── pybindings                  # Python api for executorch runtime.
+|   ├── pytree                      # C++ and Python flattening and unflattening lib for pytrees.
+|   ├── testing_util
+├── kernels                         #  1st party kernel implementations.
+|   ├── aten
+|   ├── optimized
+|   ├── portable                    #  Reference implementations of ATen operators.
+|   ├── prim_ops                    #  Special ops used in executorch runtime for control flow and symbolic primitives.
+|   ├── quantized
+├── profiler                        #  Utilities for profiling. TODO delete in favor of ETDump in sdk/
+├── runtime                         #  core cpp runtime of executorch
+|   ├── backend                     #  Backend definition and registration.
+|   ├── core                        #  Core structures used across all levels of the runtime
+|   ├── executor                    #  Model loading, initalization, and execution.
+|   ├── kernel                      #  Kernel registration and management.
+|   ├── platform                    #  Layer between architecture specific code and user calls.
+├── schema                          #  Executorch program definition, TODO move under serialization/
+├── scripts                         #  Utility scripts for size management, dependency management, etc.
+├── sdk                             #  Model profiling, debugging, and introspection: NOT READY YET FOR OSS USE
+├── shim                            #  Compatibility layer between OSS and Internal builds
+├── test                            #  Broad scoped end2end tests
+├── third-party                     #  third-party dependencies
+├── util                            #  TODO delete this
+
 ## License
 ExecuTorch is BSD licensed, as found in the LICENSE file.