build: rpm + deb targets, build-in-docker targets, CircleCI pipeline rewrite

Co-authored-by: Armin Wehrfritz <dkxls23@gmail.com>

docs/installation/rpm-repos.rst

@@ -0,0 +1,31 @@
+.. _installation-rpm-repos:
+
+RPM repositories
+~~~~~~~~~~~~~~~~
+
+We provide a single RPM repository for all RPM-based Linux distros.
+The zrepl binary in the repo is the same as the one published to GitHub.
+Since Go binaries are statically linked, the RPM should work about everywhere.
+
+The fingerprint of the signing key is ``F6F6 E8EA 6F2F 1462 2878 B5DE 50E3 4417 826E 2CE6``.
+It is available at `<https://zrepl.cschwarz.com/rpm/rpm-key.asc>`_ .
+Please open an issue on GitHub if you encounter any issues with the repository.
+
+Copy-paste the following snippet into your shell to set up the zrepl repository.
+Then ``dnf install zrepl`` and make sure to confirm that the signing key matches the one shown above.
+
+.. literalinclude:: ../../packaging/rpm/zrepl.repo
+::
+
+    cat > /etc/yum.repos.d/zrepl.repo <<EOF
+    [zrepl]
+    name = zrepl
+    baseurl = https://zrepl.cschwarz.com/rpm/repo
+    gpgkey = https://zrepl.cschwarz.com/rpm/rpm-key.asc
+    EOF
+
+.. NOTE::
+
+   Until zrepl reaches 1.0, the repository will be updated to the latest zrepl release immediately.
+   This includes breaking changes between zrepl versions.
+   If that bothers you, use the `dnf versionlock plugin <https://dnf-plugins-core.readthedocs.io/en/latest/versionlock.html>`_ to pin the version of zrepl on your system.