Add Radarr Cloudron app packaging

- Add CloudronManifest.json with app configuration
- Add Dockerfile for building Radarr image
- Add start.sh script to launch Radarr
- Add icon.png for app icon
- Update README.md with installation and usage instructions

Dockerfile

@@ -0,0 +1,17 @@
+FROM --platform=amd64 cloudron/base:4.2.0@sha256:46da2fffb36353ef714f97ae8e962bd2c212ca091108d768ba473078319a47f4
+
+RUN apt-get update -y && \
+    apt install -y curl sqlite3 dpkg wget
+
+RUN mkdir -p /app/code/radarr
+WORKDIR /app/code
+
+RUN wget --content-disposition "http://radarr.servarr.com/v1/update/master/updatefile?os=linux&runtime=netcore&arch=x64" && \
+    tar -xvzf Radarr*.linux*.tar.gz -C /app/code/radarr && \
+    rm -f Radarr*.linux*.tar.gz
+
+COPY start.sh /app/code/
+RUN chmod +x /app/code/start.sh && \
+    chown -R cloudron:cloudron /app/code/radarr
+
+CMD [ "/app/code/start.sh" ]