Merge branch 'docs/secure-reorg-intro' into 'master'

Add initial doc on new security page

Closes #10865

See merge request gitlab-org/gitlab-ee!10548

doc/user/security/index.md

+---
+is_hidden: true
+---
+
+# GitLab Secure
+
+Check your application for security vulnerabilities that may lead to unauthorized access,
+data leaks, and denial of services. GitLab will perform static and dynamic tests on the
+code of your application, looking for known flaws and report them in the merge request
+so you can fix them before merging. Security teams can use dashboards to get a
+high-level view on projects and groups, and start remediation processes when needed.
+
+The following documentation relates to the DevOps **Secure** stage:
+
+| Secure topics                                                                                   | Description                                                            |
+|:------------------------------------------------------------------------------------------------|:-----------------------------------------------------------------------|
+| [Container Scanning](../project/merge_requests/container_scanning.md) **[ULTIMATE]**            | Use Clair to scan docker images for known vulnerabilities.             |
+| [Dependency Scanning](../project/merge_requests/dependency_scanning.md) **[ULTIMATE]**          | Analyze your dependencies for known vulnerabilities.                   |
+| [Dynamic Application Security Testing (DAST)](../project/merge_requests/dast.md) **[ULTIMATE]** | Analyze running web applications for known vulnerabilities.            |
+| [Group Security Dashboard](../group/security_dashboard/index.md) **[ULTIMATE]**                 | View vulnerabilities in all the projects in a group and its subgroups. |
+| [License Management](../project/merge_requests/license_management.md) **[ULTIMATE]**            | Search your project's dependencies for their licenses.                 |
+| [Project Security Dashboard](../project/security_dashboard.md) **[ULTIMATE]**                   | View the latest security reports for your project.                     |
+| [Static Application Security Testing (SAST)](../project/merge_requests/sast.md) **[ULTIMATE]**  | Analyze source code for known vulnerabilities.                         |