Add CMD so that NGINX log appears in container log.

Config/F-DroidRepo/Dockerfile

@@ -135,3 +135,7 @@ RUN cp -rv "$FDROID" "$WEBROOT/"
 # TODO: Can NGINX be configured to serve this as root while still
 #       having the URL be fdroid/repo/? How do others handle this?
 RUN cp -rv "$REPO"/* "$WEBROOT/"
+
+CMD echo "F-Droid Repository has been started!" && \
+      tail -F /var/log/nginx/access.log & \
+      tail -F /var/log/nginx/error.log