Create new detection rule set documentation to be included in the new docs.

docs/docset.yml

@@ -0,0 +1,16 @@
+project: 'detection rules'
+cross_links:
+  - docs-content
+exclude:
+  - '_*.md'
+  - 'README.md'
+subs:
+  stack: Elastic Stack
+
+extensions:
+  - detection-rules
+
+toc:
+  - file: index.md
+    detection_rules: ['../rules', '../rules_building_block']
+

docs/index.md

@@ -0,0 +1,3 @@
+# Detection rules
+
+Landing / overview page