Move and expand push gateway description.

content/docs/practices/pushing.md → content/docs/instrumenting/pushing.md

 ---
-title: Pushing data
-sort_rank: 2
+title: Pushing metrics
+sort_rank: 3
 ---
 
-# Pushing Data
+# Pushing metrics
 
-Occasionally you will need to monitor components which cannot be scraped: They
-might be behind a firewall, or they might be too short-lived to expose data
+Occasionally you will need to monitor components which cannot be scraped. They
+might live behind a firewall, or they might be too short-lived to expose data
 reliably via the pull model. The
-[push gateway](https://github.com/prometheus/pushgateway) allows you to push
+[Prometheus push gateway](https://github.com/prometheus/pushgateway) allows you to push
 time series from these components to an intermediary job which Prometheus can
-scrape.
+scrape. Combined with Prometheus's simple text-based exposition format, this
+makes it easy to instrument even shell scripts without a client library.
 
-For more information on installing and using the push gateway, see the
-project's
+For more information on using the push gateway, see the project's
 [README.md](https://github.com/prometheus/pushgateway/blob/master/README.md).