Added a build example.

Not complete, really just a dump of some code I had lying around.

example/Dockerfile

+FROM adarnimrod/elementaryos
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y \
+        debhelper \
+        libebook1.2-dev \
+        libecal1.2-dev \
+        libedataserver1.2-dev \
+        libflatpak-dev \
+        libghc-gnutls-dev \
+        libnotify-dev \
+        libsqlite3-dev \
+        libunity-dev \
+    && \
+    rm -rf /tmp/* /var/tmp/* /var/lib/apt/lists/* /var/cache/apt/archives/*
+ENV DESTDIR=/usr \
+    MESON_INSTALL_PREFIX=/usr
+VOLUME /volume
+WORKDIR /volume
+USER 1000
+ENTRYPOINT ["sh", "-c"]
+CMD ["meson build --buildtype=release && ninja -C build && glib-compile-schemas ./data/"]

example/README.md

+# ElementaryOS applications
+
+> Build ElementaryOS applications.
+
+## Build
+
+```
+docker-compose up --build
+```
+
+## Run
+
+Inside the application's directory:
+
+```
+GSETTINGS_SCHEMA_DIR=data build/io.elementary.<APPLICATION_NAME>
+```

example/docker-compose.yml

+# vim:ff=unix:ts=2:sw=2:ai:expandtab:ft=yaml
+---
+version: '3.5'
+services:
+  conecto:
+    build:
+      context: ./
+    volumes:
+      - ./conecto:/volume
+  tasks:
+    build:
+      context: ./
+    volumes:
+      - ./tasks:/volume
+  sideload:
+    build:
+      context: ./
+    volumes:
+      - ./sideload:/volume