Add README to the esp32 example

examples/esp32/README.md

@@ -0,0 +1,19 @@
+# An example ESP32 application
+
+To build this application, follow these steps:
+
+1. Make sure you have Docker installed
+2. Clone whole mongoose repository on your machine:
+  ```sh
+  git clone --depth 1 https://github.com/cesanta/mongoose.git
+  ```
+3. Start command line or terminal, and go into the example's directory:
+  ```sh
+  cd mongoose/examples/esp32
+  ```
+4. Run `make`. This invokes a Docker-based build. A firmware will be built
+  in the `build/` directory:
+  ```sh
+  make
+  ```
+