Remove contribute.json info from guidelines

[janbrasna]

Resolves #186

+ updates one more tls config link in cheatsheet,
+ fixes cheatsheet order.

(I hope № 13 was not left out intentionally like in an elevator;) so I've fixed the cheat sheet order gap since #183 along the way)

[janbrasna]

BTW to make further additions/removals like this easier, I can also dumb down the markdown numbered list to:

# Table of Contents
1. [Cheat Sheet](#web-security-cheat-sheet)
1. [Transport Layer Security (TLS/SSL)](#transport-layer-security-tlsssl)
    1. [HTTPS](#https)
    1. [HTTP Strict Transport Security](#http-strict-transport-security)
    1. [HTTP Redirections](#http-redirections)
    1. [Resource Loading](#resource-loading)
1. [Content Security Policy](#content-security-policy)
1. [Cookies](#cookies)
1. [Cross-origin Resource Sharing](#cross-origin-resource-sharing)
1. [CSRF Prevention](#csrf-prevention)
1. [Referrer Policy](#referrer-policy)
1. [robots.txt](#robotstxt)
1. [Subresource Integrity](#subresource-integrity)
1. [X-Content-Type-Options](#x-content-type-options)
1. [X-Frame-Options](#x-frame-options)
1. [Version History](#version-history)

to let the parser do the math and not bother authors with it:

(rendered from above:)

1. Cheat Sheet
2. Transport Layer Security (TLS/SSL)
   1. HTTPS
   2. HTTP Strict Transport Security
   3. HTTP Redirections
   4. Resource Loading
3. Content Security Policy
4. Cookies
5. Cross-origin Resource Sharing
6. CSRF Prevention
7. Referrer Policy
8. robots.txt
9. Subresource Integrity
10. X-Content-Type-Options
11. X-Frame-Options
12. Version History