docs: bring the README's feature tour into the plugin era

The Core Features section still presented clock/weather/sports/stocks/
music displays as built into the project, when all of them are store
plugins installed from the ledmatrix-plugins monorepo — only
starlark-apps and web-ui-info ship in this repo. The intro now says so
(the showcase itself is unchanged; those are real displays available in
the store). The display_durations reference drops its built-in-calendar
example in favor of plugin-id keys, and the Configuration section links
the new CONFIG_REFERENCE.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SXb4mKcAkVaxkeTb3YnAdr

README.md

@@ -50,7 +50,14 @@ I'm trying to be open to constructive criticism and support, as long as it's a r
 
 <details>
 <summary>Core Features</summary>
-The following plugins are available inside of the LEDMatrix project. These modular, rotating Displays that can be individually enabled or disabled per the user's needs with some configuration around display durations, teams, stocks, weather, timezones, and more. Displays include:
+LEDMatrix is a plugin platform: the displays below are plugins installed
+from the built-in Plugin Store (web interface → Plugins), where each can be
+individually enabled, ordered, and configured — display durations, teams,
+stocks, weather, timezones, and more. The core repo ships with just two
+bundled plugins (`starlark-apps` and `web-ui-info`); everything else lives
+in the [ledmatrix-plugins](https://github.com/ChuckBuilds/ledmatrix-plugins)
+monorepo and installs with one click. Displays available in the store
+include:
 
 ### Time and Weather
 - Real-time clock display (2x 64x32 Displays 4mm Pixel Pitch)
@@ -372,6 +379,10 @@ This single script installs services, dependencies, configures permissions and s
 
 ### Initial Setup
 
+For a complete list of every key in `config.json` and
+`config_secrets.json`, see
+[docs/CONFIG_REFERENCE.md](docs/CONFIG_REFERENCE.md).
+
 For most settings I recommend using the web interface:
 Edit the project via the web interface at http://[IP ADDRESS or HOSTNAME]:5000 or http://ledpi:5000 .
 
@@ -610,12 +621,7 @@ These settings control runtime behavior and GPIO timing:
 
 ### Display Durations (`display.display_durations`)
 
-Controls how long each display module stays visible in seconds before switching to the next one.
-
-- **`calendar`** (integer, default: 30)
-  - Duration in seconds for the calendar display
-  - Increase for more time to read dates/events
-  - Decrease to cycle through other displays faster
+Controls how long each installed plugin stays visible in seconds before switching to the next one, keyed by plugin id.
 
 - **Plugin-specific durations**
   - Each plugin can have its own duration setting