Added license and docs

LICENSE

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+Copyright 2019 Denis "ftc" Denisov
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.

README.md

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+# rpi_dht_modbus - Simple server to provide Modbus TCP access to DHT sensor series.
+
+## Introduction
+
+This is a combination of [Adafruit DHT library](https://github.com/adafruit/Adafruit_Python_DHT) and
+[pymodbus](https://github.com/riptideio/pymodbus) Modbus stack.
+
+The server runs as a Modbus TCP server and gives access to DHT sensors value via Modbus registers.
+
+## Installation
+
+You will need Python version 3 (tested on RPi model B with Python 3.5) with `virtualenv` module.
+After repository cloning run:
+```
+virtualenv venv
+source ./venv/bin/activate
+pip install -r requirements.txt
+```
+
+After that you will have all needed libraries so the last step is to copy `config.json.sample`
+into `config.json` and adjust it to your needs.
+