CLI, debian, make: misc cleanup and changes (#336)

This PR	groups misc cleanup and changes from https://github.com/ooni/probe-cli/pull/331.

* CLI/linux/build: add documentation

* debian/.gitignore: ignore generated files

* debian/TODO: unnecessary at this point

* debian/ooniprobe-cli.service: remove commented out lines

* debian/rules: remove unnecessary actions

* make: reindent and fix spelling

* smoketest.sh: don't run in verbose mode

Part of https://github.com/ooni/probe/issues/1466

CLI/linux/build

@@ -1,4 +1,7 @@
 #!/bin/sh
+# This script is executed by `./make` when building inside
+# an Alpine Linux docker container. Using Alpine Linux, which
+# uses musl libc, allows us to emit static binaries.
 set -e
 if [ "$GOARCH" = "" ]; then
     echo 'fatal: $GOARCH is not set' 1>&2