docs: move security article to a new 'articles' section

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

docs/sources/articles/index.rst

@@ -0,0 +1,12 @@
+:title: Docker articles
+:description: various articles related to Docker
+:keywords: docker, articles
+
+.. _articles_list:
+
+Contents:
+
+.. toctree::
+   :maxdepth: 1
+
+   security

docs/sources/installation/index.rst

@@ -31,5 +31,4 @@ Contents:
    google
    kernel
    binaries
-   security
    upgrading

docs/sources/toctree.rst

@@ -15,6 +15,8 @@ This documentation has the following resources:
    use/index
    examples/index
    reference/index
+   commandline/index
    contributing/index
    terms/index
    faq
+   articles/index