Installation guide for PlatformIO (#7142)

Author: ivankravets

doc/installing.rst

@@ -230,3 +230,20 @@ Instructions - Other OS
        cd hardware\esp8266com\esp8266
        git status
        git pull
+
+Using PlatformIO
+----------------
+
+[PlatformIO](https://platformio.org?utm_source=github&utm_medium=arduino-esp8266) is an open source ecosystem for IoT
+development with a cross-platform build system, a library manager, and full support
+for Espressif (ESP8266) development. It works on the following popular host operating systems: macOS, Windows,
+Linux 32/64, and Linux ARM (like Raspberry Pi, BeagleBone, CubieBoard).
+
+- [What is PlatformIO?](https://docs.platformio.org/en/latest/what-is-platformio.html?utm_source=github&utm_medium=arduino-esp8266)
+- [PlatformIO IDE](https://platformio.org/platformio-ide?utm_source=github&utm_medium=arduino-esp8266)
+- [PlatformIO Core](https://docs.platformio.org/en/latest/core.html?utm_source=github&utm_medium=arduino-esp8266) (command line tool)
+- [Advanced usage](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=github&utm_medium=arduino-esp8266) -
+  custom settings, uploading to SPIFFS, Over-the-Air (OTA), staging version
+- [Integration with Cloud and Standalone IDEs](https://docs.platformio.org/en/latest/ide.html?utm_source=github&utm_medium=arduino-esp8266) -
+  Cloud9, Codeanywhere, Eclipse Che (Codenvy), Atom, CLion, Eclipse, Emacs, NetBeans, Qt Creator, Sublime Text, VIM, Visual Studio, and VSCode
+- [Project Examples](https://docs.platformio.org/en/latest/platforms/espressif8266.html?utm_source=github&utm_medium=arduino-esp8266#examples)