Update docker FAQ (influxdata#7868)

Author: danielnelson

docs/FAQ.md

@@ -5,19 +5,14 @@
 You will need to setup several volume mounts as well as some environment
 variables:
 ```
-docker run --name telegraf
-	-v /:/hostfs:ro
-	-v /etc:/hostfs/etc:ro
-	-v /proc:/hostfs/proc:ro
-	-v /sys:/hostfs/sys:ro
-	-v /var:/hostfs/var:ro
-	-v /run:/hostfs/run:ro
-	-e HOST_ETC=/hostfs/etc
-	-e HOST_PROC=/hostfs/proc
-	-e HOST_SYS=/hostfs/sys
-	-e HOST_VAR=/hostfs/var
-	-e HOST_RUN=/hostfs/run
-	-e HOST_MOUNT_PREFIX=/hostfs
+docker run --name telegraf \
+	-v /:/hostfs:ro \
+	-e HOST_ETC=/hostfs/etc \
+	-e HOST_PROC=/hostfs/proc \
+	-e HOST_SYS=/hostfs/sys \
+	-e HOST_VAR=/hostfs/var \
+	-e HOST_RUN=/hostfs/run \
+	-e HOST_MOUNT_PREFIX=/hostfs \
 	telegraf
 ```