Update docker kill reference docs

- explain the either "name" or "id" can be used to reference a container
- explain that signals can be sent by name or number

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/kill.md

@@ -27,9 +27,45 @@ Options:
 
 ## Description
 
-The main process inside the container will be sent `SIGKILL`, or any
-signal specified with option `--signal`.
+The `docker kill` subcommand kills one or more containers. The main process
+inside the container is sent `SIGKILL` signal (default), or the signal that is
+specified with the `--signal` option. You can kill a container using the
+container's ID, ID-prefix, or name.
 
 > **Note**: `ENTRYPOINT` and `CMD` in the *shell* form run as a subcommand of
 > `/bin/sh -c`, which does not pass signals. This means that the executable is
 > not the container’s PID 1 and does not receive Unix signals.
+
+## Examples
+
+
+### Send a KILL signal  to a container
+
+The following example sends the default `KILL` signal to the container named
+`my_container`:
+
+```bash
+$ docker kill my_container
+```
+
+### Send a custom signal  to a container
+
+The following example sends a `SIGHUP` signal to the container named
+`my_container`:
+
+```bash
+$ docker kill --signal=SIGHUP  my_container
+```
+
+
+You can specify a custom signal either by _name_, or _number_. The `SIG` prefix
+is optional, so the following examples are equivalent:
+
+```bash
+$ docker kill --signal=SIGHUP my_container
+$ docker kill --signal=HUP my_container
+$ docker kill --signal=1 my_container
+```
+
+Refer to the [`signal(7)`](http://man7.org/linux/man-pages/man7/signal.7.html)
+man-page for a list of standard Linux signals.