Created PlatformIO CLI (markdown)

PlatformIO-CLI.md

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+How to flash the Tasmota firmware onto a device using the `platformio` command line interface on Linux. This manual was tested on Ubuntu 17.10.
+
+# Prerequisites
+## Install Python and PIP
+```
+sudo apt-get install python-pip
+```
+
+## Install PlatformIO CLI
+```
+sudo pip install -U platformio
+```
+
+## Download the Sonoff-Tasmota source code
+
+Either download the latest Tasmota release Source code from https://github.com/arendst/Sonoff-Tasmota/releases and extract it or clone the Git repository:
+```
+git clone https://github.com/arendst/Sonoff-Tasmota.git
+```
+
+## Select the environment
+Edit the file `platformio.ini` and uncomment one of the `env_default` lines by removing the `;`, eg.:
+```
+; *** Uncomment one of the lines below to build/upload only one environment
+env_default = sonoff
+;env_default = sonoff-CN
+;env_default = sonoff-DE
+;env_default = sonoff-ES
+;env_default = sonoff-FR
+;env_default = sonoff-IT
+;env_default = sonoff-NL
+;env_default = sonoff-PL
+;env_default = sonoff-minimal
+;env_default = sonoff-ds18x20
+```
+
+# Compile and upload
+Once all the prerequisites are in place compiling and uploading is one simple command. Execute this from within the `Sonoff-Tasmota` source code directory:
+```
+platformio run --target upload --upload-port /dev/ttyXYZ
+```
+Just make sure to replace `/dev/ttyXYZ` with [the actual serial port](https://unix.stackexchange.com/questions/144029/command-to-determine-ports-of-a-device-like-dev-ttyusb0) your device is connected to.
+
+Depending on your configuration your user account [may need to be in the `dialout` group](https://askubuntu.com/questions/112568/how-do-i-allow-a-non-default-user-to-use-serial-device-ttyusb0).