Remove placeholder square brackets in FAQ entry.

Since it's plural now, it's no longer a placeholder.

content/docs/introduction/faq.md

@@ -12,7 +12,7 @@ toc: full-width
 Prometheus is an open-source systems monitoring and alerting toolkit
 with an active ecosystem. See the [overview](/docs/introduction/overview/).
 
-### How does Prometheus compare against \[other monitoring systems\]?
+### How does Prometheus compare against other monitoring systems?
 
 See the [comparison](/docs/introduction/comparison/) page.