docker: update dev env and documentation

system/run-aptly-cmd

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+# cleanup
+rm -rf /app/tmp
+rm -rf /tmp/aptly*
+
+usermod -u `stat -c %u /app` aptly >/dev/null
+chown -R `stat -c %u /app` /var/lib/aptly
+
+# use same /home/runner dir as in github workflow
+chown -R `stat -c %u /app` /home/runner
+
+cmd=$@
+if [ -z "$cmd" ]; then
+    cmd="bash"
+fi
+su aptly -c "cd /app; export HOME=/home/runner; export PATH=\$PATH:/app/build; $cmd"