feat: add Arduino App specification document

Author: dido18

docs/app-specification.md

@@ -0,0 +1,43 @@
+# Arduino App specification
+This is the specification for the `Arduino App` (from now on called App) format to be used with `arduino-app-cli`.
+
+An App is a self-contained folder that includes the following components:
+ - `app.yaml` (mandatory) the file descriptor of the  app in YAML format.
+ - `sketch` (optional) the folder containing an Arduino [Sketch](https://arduino.github.io/arduino-cli/1.3/sketch-specification/))
+ - `python` (optional) the folde containin the Python code
+
+The App must be self-contained (it does not contain references to external files) because this means it can be exported, shared, or zipped easily.
+
+## Arduino App Folder structure
+```
+myapp/
+    app.yaml
+    sketch/
+        sketch.ino
+        sketch.yaml
+    python/
+        main.py
+        requirements.txt
+```
+
+
+## App descriptor file
+The `app.yaml` is the YAML  specificaiotn of an APP.
+
+- `name` - the name of the app.
+```yaml
+name: My Arduino App
+description: An example app showcasing what you can do
+icon: 🍓
+
+bricks:
+  - arduino/dbstorage:
+      variables:
+        ROOT_PASSWORD: ${secret.db_password}
+        PORT: 8080
+  - arduino/text-generation:
+      model: gemma-1
+  - arduino/objectdetection:
+      model: yolo
+  - arduino/mqtt
+```