Architecture documentation for Configurator and API (#13935)

* Architecture documentation for the configurator and api

* Apply suggestions from code review

Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>

Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>

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+# QMK Configurator Architecture
+
+This page describes the web architecture behind QMK Configurator at a high level. If you are interested in the architecture of the QMK Configurator code itself you should start at the [qmk_configurator](https://github.com/qmk/qmk_configurator) repository.
+
+# Overview
+
+![QMK Configurator Architecture Diagram](configurator_diagram.svg)
+
+# Detailed Description
+
+QMK Configurator is a [Single Page Application](https://en.wikipedia.org/wiki/Single-page_application) that allows users to create custom keymaps for their QMK-compatible keyboard. They can export JSON representation of their keymaps and compile firmware binaries that can be flashed to their keyboard using a tool like [QMK Toolbox](https://github.com/qmk/qmk_toolbox).
+
+Configurator gets metadata about keyboards from the Keyboard Metadata store and submits compile requests to the QMK API. The results of those compile requests will be made available on [Digital Ocean Spaces](https://www.digitalocean.com/products/spaces/), an S3-compatible data store.
+
+## Configurator Frontend
+
+Address: <https://config.qmk.fm>
+
+The [Configurator Frontend](https://config.qmk.fm) is compiled into a set of static files that are served by Github Pages. This action happens every time a commit is pushed to the [qmk_configurator `master`](https://github.com/qmk/qmk_configurator) branch. You can view the status of these jobs on the [qmk_configurator actions tab](https://github.com/qmk/qmk_configurator/actions/workflows/build.yml).
+
+## Keyboard Metadata
+
+Address: <https://keyboards.qmk.fm>
+
+The Keyboard Metadata is generated every time a keyboard in [qmk_firmware](https://github.com/qmk/qmk_firmware) changes. The resulting JSON files are uploaded to Spaces and used by Configurator to generate UI for each keyboard. You can view the status of this job on the [qmk_firmware actions tab](https://github.com/qmk/qmk_firmware/actions/workflows/api.yml). If you are a QMK Collaborator you can manually run this job using the `workflow_dispatch` event trigger.
+
+## QMK API
+
+Address: <http://api.qmk.fm>
+
+The QMK API accepts `keymap.json` files for compilation. These are the same files you can use directly with `qmk compile` and `qmk flash`. When a `keymap.json` is submitted the browser will poll the status of the job periodically (every 2 seconds or longer, preferably) until the job has completed. The final status JSON will contain pointers to source and binary downloads for the keymap.
+
+QMK API always presents the source and binary downloads side-by-side to comply with the GPL.
+
+There are 3 non-error status responses from the API-
+
+1. Compile Job Queued
+2. Compile Job Running
+3. Compile Job Finished
+
+### Compile Job Queued
+
+This status indicates that the job has not yet been picked up by a [QMK Compiler](#qmk-compiler) node. Configurator shows this status as "Waiting for an oven".
+
+### Compile Job Running
+
+This status indicates that the job has started compiling. Configurator shows this status as "Baking".
+
+### Compile Job Finished
+
+This status indicates that the job has completed. There will be keys in the status JSON for source and binary downloads.
+
+## Redis/RQ
+
+QMK API uses RQ to distribute jobs to the available [QMK Compiler](#qmk-compiler) nodes. When a `keymap.json` is received it's put into the RQ queue, where a `qmk_compiler` node will pick it up from.
+
+## QMK Compiler
+
+[QMK Compiler](https://github.com/qmk/qmk_compiler) is what actually performs the compilation of the `keymap.json`. It does so by checking out the requested `qmk_firmware` branch, running `qmk compile keymap.json`, and then uploading the resulting source and binary to Digital Ocean Spaces. 
+
+When users download their source/binary, API will redirect them to the authenticated Spaces download URL.