Add README.md

Author: mskvortsov

README.md

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+## Platformio packages with custom-built SDK libraries
+
+Runs [esp32-arduino-lib-builder](https://hub.docker.com/r/espressif/esp32-arduino-lib-builder) docker image by first appending esp-idf sdkconfigs with contents of corresponding files from the `configs/` directory.
+
+To make a release, push a new tag. Release produces two zip files, one for arduino-esp32 v2 and another for v3.
+
+Using with arduino-esp32 v2:
+```
+platform = platformio/espressif32@6.8.1
+platform_packages =
+  platformio/framework-arduinoespressif32@https://.../esp32-2.0.17.zip
+```
+
+Using with arduino-esp32 v3:
+```
+platform = platformio/espressif32@6.8.1
+platform_packages =
+  platformio/framework-arduinoespressif32@https://github.com/espressif/arduino-esp32/releases/download/3.0.4/esp32-3.0.4.zip
+  platformio/framework-arduinoespressif32-libs@https://.../esp32-arduino-libs.zip
+```