This updates the mkdocs.yml source file such that the HTTP Preferences
API is included in the website navigation bar and in the HTTP API
overview page.

This commit also refreshes the docs/README.md file with more verbose
instructions for building and viewing the documentation locally.

* Original issue: #5069 Document org & user preferences HTTP docs
* Original PR: #5087

Closes #5193

Conflicts:
	public/app/features/templating/templateValuesSrv.js

fix(templating): fixed issue with  value being shown instead of it's text representation, fixes #5172

Authorization header to X-DS-Authorization in backend_srv.js

fix(templating): fixed issue with detecting data source variable in other template variable definition, fixes #5165

closes #5167

fix(templating): fixed issue with nested template variables and multi select, the child variable selection state is now updated like single select variables, so if none matches the first option is selected, fixes #4861

Conflicts:
	package.json

Commit adds missing option `Read-Only Editor` to `auto_assign_org_role` description.

Conflicts:
	pkg/api/frontendsettings.go