Update README.

README.md

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-# LoRaWAN(R) device-profiles repository
+# LoRaWAN(R) device-profiles
 
+This repository contains device-profiles for LoRaWAN devices grouped by
+vendor. A device-profile contains important information about the capabilities
+of the device. For example which LoRaWAN mac-version has been implemented,
+which regions are supported, if the device supports Class-B or Class-C, etc...
+The aim is to build a complete list of LoRaWAN device-profiles that then can
+be imported by ChirpStack or potentially any other LNS.
+
+## Why not use the TTN lorawan-devices repository?
+
+Unfortuantely the [https://github.com/thethingsnetwork/lorawan-devices](https://github.com/thethingsnetwork/lorawan-devices)
+repository can no longer be used as a whole. The open-source license has been
+removed and users are not allowed to _extract and/or reuse the Device Repositoryas
+as a whole or a substantial part of its content_.
+This prevents ChirpStack users (and other LNS providers) from importing this
+repository into their database.
+
+The goal of this repository is to provide an open-source database of LoRaWAN
+device-profiles that can be freely imported.
+
+## Structure
+
+Example structure for an `example-vendor` with an `example` device:
+
+```
+vendors/
+└── example-vendor
+    ├── codecs
+    │   ├── example.js
+    │   ├── test_decode_example.json
+    │   └── test_encode_example.json
+    ├── devices
+    │   └── example.toml
+    ├── profiles
+    │   └── example-EU868.toml
+    └── vendor.toml
+```
+
+Please take a look at the `vendors/example-vendor` example documented
+configuration files.
+
+### `vendors/example-vendor`
+
+This is the root of the example vendor. It must contain a `vendor.toml`
+file. This `vendor.toml`.
+
+### `vendors/example-vendor/codecs`
+
+This directory contains the payload codecs. Codecs can be used by one or
+multiple devices. E.g. some vendors have a generic payload codec.
+
+Each codec is expected to have tests for encoding and decoding. If the
+codec filename is `example.js`, then you should create two test-files
+called `test_decode_example.json` (thus + `test_decode_` prefix and `.json`
+extension) and `test_encode_example.json`.
+
+### `vendors/example-vendor/devices`
+
+This directory contains the devices. Each device will have its own `.toml`
+configuration.
+
+### `vendors/example-vendor/profiles`
+
+This directory contains the profiles. These profiles can be used by one
+or multiple devices. The profile also defines the region.
+
+## Running the test
+
+To run the test-runner, execute:
+
+```
+make test
+```
+
+This will run all tests within a Docker Compose environment.
+
+## License
+
+This repository is distributed under the MIT license. See also `LICENSE`.