Add manual page.

This is mostly copy+paste from the README.md.

.gitignore

@@ -11,3 +11,5 @@ depcomp
 install-sh
 main.o
 missing
+clr-service-restart.1
+clr-service-restart-*.tar*

Makefile.am

@@ -1,6 +1,11 @@
 
+clr-service-restart.1: clr-service-restart.1.md
+	ronn -r $< --pipe > $@
+
 bin_PROGRAMS = clr-service-restart
 
 clr_service_restart_SOURCES = \
 	main.c
 
+dist_man_MANS = \
+	clr-service-restart.1

clr-service-restart.1.md

@@ -0,0 +1,129 @@
+clr-service-restart(1) -- restarts systemd services after updates
+=================================================================
+
+## SYNOPSIS
+
+`/usr/bin/clr-service-restart`
+
+
+## FILES
+
+`/etc/clr-service-restart`
+`/usr/share/clr-service-restart`
+
+
+## DESCRIPTION
+
+The Linux kernel maintains information about running processes in the
+`procfs` filesystem. This information can be used to identify processes
+that are using resources that are no longer physically present on
+the file system, such as when a binary or system library is updated.
+
+Any software update causes the kernel to see that a reference to a
+binary or a reference to a library is no longer corresponding with the
+actual current version of the library or binary on the filesystem. If
+this happens, the kernel will mark the `procfs` entries for those
+references as `(deleted)`. Specifically the `exe` symlink will get
+marked in this way if the binary is updated, and the `maps` file will
+get updated in this way if a library component is updated.
+
+Using these references, we now know which programs are currently being
+executed that are holding references to outdated libraries or binaries,
+and therefore should be restarted.
+
+However, we do not want to restart programs that are not part of a
+system unit, or in some other way are not part of the system domain. In
+order to avoid considering all processes running for the purpose of
+restarting them, we restrict consideration to only those processes
+that are listed as active `tasks` in the systemd `system.slice`
+hierarchy maintained under `/sys/fs/cgroup/systemd/`. This hierarchy
+only contains units (and therefore tasks) in the system domain and
+excludes user units or user programs.
+
+It's extremely risky to restart all units unconditionally since some
+units may require specific ordering, interaction or other factors
+to be considered. By default, this program will not restart any
+service automatically, and will only consider units that have been
+explicitly marked as `allowed` by either the local administrator
+or the distribution. This is done through maintaining symlinks in
+`/usr/share/clr-service-restart` and `/etc/clr-service-restart`. If a
+valid symlink is found in these folders, the unit will be considered
+for restarting. If a symlink is found in `/etc/clr-service-restart`
+with the name of a unit pointing to `/dev/null` it will be
+omitted for consideration and not be restarted. Links in the
+`/etc/clr-service-restart` location take precedence over those in
+`/usr/share/clr-service-restart`. Links to `/dev/null` in the
+`/usr/share/clr-service-restart` location are invalid.
+
+
+## COMMANDS
+
+These symlinks can be manipulated by the local administrator with the
+`clr-service-restart` program, which understands the following 3
+commands:
+
+ * `allow "foo.service"`:
+
+   Mark "foo.service" as restartable.
+
+ * `disallow "bar.service"`:
+
+   Mark "bar.service" as not restartable.
+
+ * `default "baz.service"`:
+
+   Remove local preferences and revert to the distribution default
+   for "baz.service".
+
+If `clr-service-restart` is executed without any commands, it will
+restart all services that are marked `allow` for restart.
+
+
+## OPTIONS
+
+The following options are understood. These options may not be used
+together with the `allow`, `disallow` and `default` commands.
+
+ * `-n`:
+
+   Don't actually perform any restarts, just show what would happen
+   if the program would execute normally. This makes the program
+   more verbose.
+
+ * `-a`:
+
+   Consider all system units. With this option, all system units that
+   are running will be considered for restarting. This should normally
+   only be done interactively, and never in an automated fashion.
+
+
+## BUGS
+
+Please report bugs to: `[email protected]`
+
+
+## COPYRIGHT
+
+Copyright © 2018 Intel Corporation
+
+Author: Auke-jan H. Kok `<[email protected]>`
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published
+by the Free Software Foundation, either version 3 of the License,
+or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+
+## SEE ALSO
+
+`systemd(1)`, `procfs(5)`
+
+`systemd-cgls -u system.slice`