Add documentation for the filters

docs/docs/intro.md

@@ -6,3 +6,4 @@ slug: /
 Read more about:
 
 * [Namespaces](/namespaces)
+* [Search features](/search-features)

docs/docs/search.md

@@ -0,0 +1,14 @@
+---
+title: Search features
+slug: search-features
+---
+
+While searching for packages you may want to refine the search terms with modifiers. 
+Currently, the following modifiers are available:
+
+* `depends:<@namespace>/<packagename>`: Shows the dependents page for a package
+* `in:<@namespace> <packagename>`: Searches for a package name in the specified namespace
+* `in:<@namespace>`: Lists packages in a namespace
+
+These modifiers must be placed at the very beginning of the search query, otherwise they will
+be interpreted as a search term.