docs: document config-mode modules

docs/dev/configmode.rst

+Config Mode
+===========
+
+As of 2014.4 `gluon-config-mode` consists of several modules.
+
+gluon-config-mode-core
+    This modules provides the core functionality for the config mode.
+    All modules must depend on it.
+
+gluon-config-mode-hostname
+    Provides a hostname field.
+
+gluon-config-mode-autoupdater
+    Informs whether the autoupdater is enabled.
+
+gluon-config-mode-mesh-vpn
+    Allows toggling of mesh-vpn-fastd and setting a bandwidth limit.
+
+gluon-config-mode-geo-location
+    Enables the user to set the geographical location of the node.
+
+gluon-config-mode-contact-info
+    Adds a field where the user can provide contact information.
+
+In order to get a config mode close to the one found in 2014.3.x you may add
+these modules to your `site.mk`:
+gluon-config-mode-hostname,
+gluon-config-mode-autoupdater,
+gluon-config-mode-mesh-vpn,
+gluon-config-mode-geo-location,
+gluon-config-mode-contact-info
+
+Writing Config Mode Modules
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Config mode modules are located at `/lib/gluon/config-mode/wizard` and
+`/lib/gluon/config-mode/reboot`. Modules are named like `0000-name.lua` and
+are executed in lexical order. If you take the standard set of modules, the
+order is, for wizard modules:
+
+  - 0050-autoupdater-info
+  - 0100-hostname
+  - 0300-mesh-vpn
+  - 0400-geo-location
+  - 0500-contact-info
+
+While for reboot modules it is:
+
+  - 0100-mesh-vpn
+  - 0900-msg-reboot
+
+Wizards
+-------
+
+Wizard modules return a UCI section. A simple module capable of changing the
+hostname might look like this::
+
+  local cbi = require "luci.cbi"
+  local uci = luci.model.uci.cursor()
+
+  local M = {}
+
+  function M.section(form)
+    local s = form:section(cbi.SimpleSection, nil, nil)
+    local o = s:option(cbi.Value, "_hostname", "Hostname")
+    o.value = uci:get_first("system", "system", "hostname")
+    o.rmempty = false
+    o.datatype = "hostname"
+  end
+
+  function M.handle(data)
+    uci:set("system", uci:get_first("system", "system"), "hostname", data._hostname)
+    uci:save("system")
+    uci:commit("system")
+  end
+
+  return M
+
+Reboot page
+-----------
+
+Reboot modules return a function that will be called when the page is to be
+rendered or nil (i.e. the module is skipped)::
+
+  if no_hello_world_today then
+    return nil
+  else
+    return function ()
+      luci.template.render_string("Hello World!")
+    end
+  end
+

docs/index.rst

@@ -36,6 +36,7 @@ Developer Documentation
 
    dev/basics
    dev/hardware
+   dev/configmode
 
 Supported Devices
 -----------------