Missing documentation

[NF997]

Just to keep track of it, the following rules miss documentation (there is currently only a placeholder file):

• detect-helmet-without-nocache
• detect-option-multiplestatements-in-mysql
• detect-option-rejectunauthorized-in-nodejs-httpsrequest
• detect-possible-timing-attacks
• disable-ssl-across-node-server

[Nantris]

@gkouziik are there plans to populate these?