Update StaticQuery documentation

To explicitly make it clear that StaticQuery should NOT be used on page components and doing so will result in a Loading (StaticQuery) message showing up on the page.

docs/docs/static-query.md

@@ -2,7 +2,7 @@
 title: "Querying data in non-page components using StaticQuery"
 ---
 
-Gatsby v2 introduces `StaticQuery`, a new API that allows non-page components to retrieve data via GraphQL query.
+Gatsby v2 introduces `StaticQuery`, a new API that allows **non-page components** to retrieve data via GraphQL query. Using this on page components will result in the message `Loading (StaticQuery)` showing up on your pages.
 
 ## Basic example