caddy-frontend: Review and improve documentation

Improvements:

 * link from README to schemas
 * drop incorrect entries in README
 * improve entries description in README
 * make parameter description more understandable in SCHEMA

software/caddy-frontend/README.caddy_frontend.rst

@@ -6,6 +6,8 @@ Frontend system using Caddy, based on apache-frontend software release, allowing
 
 Caddy Frontend works using the master instance / slave instance design. It means that a single main instance of Caddy will be used to act as frontend for many slaves.
 
+This documentation covers only specific scenarios. Most of the parameters are described in `software.cfg.json <software.cfg.json>`_.
+
 Software type
 =============
 
@@ -215,29 +217,15 @@ Example of value: "/erp5/web_site_module/hosting/"
 
 url
 ~~~
-Necessary to activate cache. ``url`` of backend to use.
-
-``url`` is an optional parameter.
+URL of the backend to use, optional but will result with non functioning slave.
 
 Example: http://mybackend.com/myresource
 
-domain
-~~~~~~
-
-Necessary to activate cache.
-
-The frontend will be accessible from this domain.
-
-``domain`` is an optional parameter.
-
-Example: www.mycustomdomain.com
-
 enable_cache
 ~~~~~~~~~~~~
 
-Necessary to activate cache.
+Enables HTTP cache, optional.
 
-``enable_cache`` is an optional parameter.
 
 health-check-*
 ~~~~~~~~~~~~~~

software/caddy-frontend/instance-caddy-input-schema.json

@@ -19,7 +19,7 @@
       "type": "string"
     },
     "domain": {
-      "description": "Base Domain for create subdomains (ie.: example.com).",
+      "description": "Domain used to generate automatic hostnames for slaves. For example 'example.com' will result with slave hostname 'slaveref.example.com'.",
       "pattern": "^([a-zA-Z0-9]([a-zA-Z0-9\\-]{0,61}[a-zA-Z0-9])?\\.)+[a-zA-Z]{2,6}$",
       "title": "Domain",
       "type": "string"