Do not notify systemd if `DESTDIR` differs from `PREFIX`

And document it, along with other installation instructions.

1 files changed, 21 insertions, 0 deletions

diff --git a/README.md b/README.md
index 92a6e95..74752e6 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,27 @@ then applying those upgrades on reboot via the [systemd Offline Updates][]
 functionality.
 
 
+## Installation
+
+A simple `make install` will install to `/usr/local` by default.
+
+You can run `make PREFIX=/new/prefix` to modify the scripts to base itself
+somewhere other than `/usr/local`, e.g. `make PREFIX=/usr`. `make install`
+will then install to that location.
+
+If you want to install to a separate location, e.g. if you're building a
+package, you can use `DESTDIR` to accomplish this, e.g.
+`make install DESTDIR=/path/to/packaging`.
+
+Under normal installs, after copying systemd service and timer units into place,
+the installation process will call `systemctl daemon-reload` and enable various
+units. If `DESTDIR` is set and different from `PREFIX`, then these steps are
+omitted.
+
+Similarly, systemd is normally notified on `make uninstall`, but again if
+`DESTDIR` is set and different from `PREFIX`, the steps are omitted again.
+
+
 ## TODO
 
 ### apt-listbugs