Add type to frontmatter

doc/security/README.md

 ---
 comments: false
+type: index
 ---
 
 # Security

doc/security/crime_vulnerability.md

+---
+type: reference
+---
+
 # How we manage the TLS protocol CRIME vulnerability
 
 > CRIME ("Compression Ratio Info-leak Made Easy") is a security exploit against
@@ -7,7 +11,7 @@ authentication cookies, it allows an attacker to perform session hijacking on an
 authenticated web session, allowing the launching of further attacks.
 ([CRIME](https://en.wikipedia.org/w/index.php?title=CRIME&oldid=692423806))
 
-### Description
+## Description
 
 The TLS Protocol CRIME Vulnerability affects compression over HTTPS, therefore
 it warns against using SSL Compression (for example gzip) or SPDY which
@@ -24,7 +28,7 @@ Although SPDY is enabled in Omnibus installations, CRIME relies on compression
 (the 'C') and the default compression level in NGINX's SPDY module is 0
 (no compression).
 
-### Nessus
+## Nessus
 
 The Nessus scanner, [reports a possible CRIME vulnerability][nessus] in GitLab
 similar to the following format:
@@ -50,7 +54,7 @@ attack nor does it check if compression is enabled. With just this approach, it
 cannot tell that SPDY's compression is disabled and not subject to the CRIME
 vulnerability.
 
-### References
+## References
 
 - Nginx ["Module ngx_http_spdy_module"][ngx-spdy]
 - Tenable Network Security, Inc. ["Transport Layer Security (TLS) Protocol CRIME Vulnerability"][nessus]

doc/security/information_exclusivity.md

+---
+type: concepts
+---
+
 # Information exclusivity
 
 Git is a distributed version control system (DVCS).

doc/security/password_length_limits.md

+---
+type: reference, howto
+---
+
 # Custom password length limits
 
 If you want to enforce longer user passwords you can create an extra Devise initializer with the steps below.