reproducible Debian: briefly explain the systemd build service worker setup

Signed-off-by: Holger Levsen <holger@layer-acht.org>

README

@@ -135,7 +135,7 @@ Installation tests inside chroot environments.
 
 * The (current) purpose of https://tests.reproducible-builds.org is to show the potential of reproducible builds for Debian - and six other projects currently. This is research, showing what could (and should) be done... check https://wiki.debian.org/ReproducibleBuilds for the real status of the project for Debian!
 
-* Currently, three suites are tested on 'amd64', 'i386', 'arm64' and 'armhf' architectures: 'testing', 'unstable' and 'experimental'. The tests are done using 'pbuilder' using link:https://wiki.debian.org/ReproducibleBuilds/ExperimentalToolchain[our toolchain] through concurrent builder jobs, 40 for 'amd64', 24 for 'i386', 32 for 'arm64' and 66 for 'armhf', which are each constantly testing packages and saving the results of these tests.
+* For Debian, three suites, 'testing', 'unstable' and 'experimental', are tested on four architectures: 'amd64', 'i386', 'arm64' and 'armhf'. The tests are done using 'pbuilder' through several concurrent workers: 40 for 'amd64', 24 for 'i386', 32 for 'arm64' and 66 for 'armhf', which are each constantly testing packages and saving the results of these tests. There's a single link:https://anonscm.debian.org/git/qa/jenkins.debian.net.git/tree/bin/reproducible_build_service.sh[systemd service] starting all of these link:https://anonscm.debian.org/git/qa/jenkins.debian.net.git/tree/bin/reproducible_worker.sh[workers] which in turn launch the actual link:https://anonscm.debian.org/git/qa/jenkins.debian.net.git/tree/bin/reproducible_build.sh[build script]. (So the actual builds and tests are happening outside the jenkins service.)
 
 * These builds on remote nodes run on very different hardware:
 ** for 'amd64' we are using four virtual machines, profitbricks-build(1+5+11+15)-amd64, which have 15 or 16 cores and 48gb ram each. These nodes are sponsored by link:https://jenkins.debian.net/userContent/thanks.html[Profitbricks].

bin/reproducible_build_service.sh

@@ -261,6 +261,7 @@ done
 #   - mostly done, except one needs to manually scroll down… (could probably be fixed with javascript…)
 # * there's also https://jenkins.debian.net/userContent/reproducible/debian/build_service/amd64_1/worker.log (for all the workers…)
 #   - no automatic reload for that yet, though. and not linked anywhere
+#   - probably together with build nodes graphs?
 # * enabling the service in update_jdn
 # * maintenance job might want to:
 #   - check for running builds using systemctl show & ps fax
@@ -269,4 +270,3 @@ done
 #   - remove cleanup_nodes.sh once this works
 #   - add support for disabling archs and for shutdown+respan of workers
 #   - add support for starting/stopping workers for specific archs
-# * document the new setup in README