Add info about shutting down Logstash

Fixes #6771

docs/static/setting-up-logstash.asciidoc

@@ -197,6 +197,8 @@ startup styles they use.  This list is intended to be informative, not exhaustiv
 | CentOS (and RHEL) 6 | <<running-logstash-upstart,upstart>> |
 |=======================================================================
 
+For info about shutting down Logstash safely, see <<shutdown>>.
+
 [[running-logstash-systemd]]
 ==== Running Logstash by Using Systemd
 

docs/static/shutdown.asciidoc

@@ -1,6 +1,38 @@
 [[shutdown]]
 === Shutting Down Logstash
 
+To shut down Logstash, use one of the following commands:
+
+* On systemd, use:
++
+[source,shell]
+----
+systemctl stop logstash
+----
+
+* On upstart, use: 
++
+[source,shell]
+----
+initctl stop logstash
+----
+
+* On sysv, use: 
++
+[source,shell]
+----
+/etc/init.d/logstash stop
+----
+
+* If you have the PID, use:
++
+[source,shell]
+----
+kill -TERM {logstash_pid}
+----
+
+==== What Happens During a Controlled Shutdown?
+
 When you attempt to shut down a running Logstash instance, Logstash performs several steps before it can safely shut down. It must:
 
 * Stop all input, filter and output plugins
@@ -30,8 +62,8 @@ Logstash safely whenever possible.
 [[shutdown-stall-example]]
 ==== Stall Detection Example
 
-In this example, slow filter execution prevents the pipeline from clean shutdown. By starting Logstash with the
+In this example, slow filter execution prevents the pipeline from performing a clean shutdown. Because Logstash is
-`--pipeline.unsafe_shutdown` flag, quitting with *Ctrl+C* results in an eventual shutdown that loses 20 events.
+started with the `--pipeline.unsafe_shutdown` flag, the shutdown results in the loss of 20 events.
 
 ========
 [source,shell]