[Data Explorer] Readme (#5273)

* Data explorer readme
* Update README.md
---------

Signed-off-by: Ashwin P Chandran <ashwinpc@amazon.com>

src/plugins/data_explorer/README.md

@@ -1,11 +1,76 @@
-# dataExplorer
+# Data Explorer
 
-A OpenSearch Dashboards plugin
+## Overview
 
----
+Data Explorer is an integral enhancement of the OpenSearch Dashboards that seeks to consolidate various data exploration facets into a unified platform. Built to provide an efficient data exploration experience, Data Explorer merges capabilities of different applications like Discover, Visbuilder, and Event Analytics into a singular platform.
+
+## Key Features
+
+1. **Unified Data Exploration**: Data Explorer acts as a consolidated platform for all data exploration tasks, aiming to provide users with a seamless and efficient environment.
+2. **Extensibility**: Provides an architecture that allows existing exploration apps to migrate with minimal changes.
+3. **Shared Utilities**: Offers components and utilities that can be shared across different views.
+
+## Architecture and Integration
+
+Data Explorer, at its core, is a shell for data exploration views. Here's a breakdown of the architecture and how it manages responsibilities:
+
+### Data Explorer Responsibilities:
+
+1. **Data Source**: Acts as the central point for the data source being explored.
+2. **View Registry**: Allows apps to register themselves as views and manages their display based on user selection.
+3. **State Management**: Provides shared state management and hooks for underlying apps to register their state reducers.
+4. **Shared Utilities**: Contains components and utilities that can be reused by various views. 
+
+### View Responsibilities:
+
+1. **Metadata Storage**: Handles the logic for storing metadata and its retrieval (Saved objects).
+2. **Data Fetching**: Manages the logic for fetching data from the data source.
+3. **View specific state management**: Handles view-specific state management and hooks into Data Explorer's state management.
+4. **Nav Options & Search/Query Bar**: Manages the navigation options, time filter, and search bar.
+5. **View Specific Logic**: Contains view-specific rendering and application logic.
+6. **Embeddables**: Responsible for registering their embeddables.
 
-## Development
+### Migrating Existing Applications:
+
+Existing applications can migrate their data exploration views to Data Explorer. Such migrations involve:
+
+1. Registering the application as a view.
+2. Using Data Explorer's state management and data source.
+3. Modifying routes to utilize Data Explorer's routes.
+4. Adapting the UI to match Data Explorer's panel and canvas components.
+
+#### Routing:
+
+Existing routes for each view are expected to redirect to new routes prefixed with `/data_explorer`. E.g., existing Discover route will redirect to `/data_explorer/discover`.
+
+### View Registry:
+
+For an application to be registered as a view within Data Explorer, it needs to adhere to the following data model:
+
+```ts
+interface ViewDefinition<T = any> {
+  readonly id: string;
+  readonly title: string;
+  readonly ui?: {
+    defaults: DefaultViewState | (() => DefaultViewState) | (() => Promise<DefaultViewState>);
+    slice: Slice<T>;
+  };
+  readonly Canvas: LazyExoticComponent<(props: ViewProps) => React.ReactElement>;
+  readonly Panel: LazyExoticComponent<(props: ViewProps) => React.ReactElement>;
+  readonly Context: LazyExoticComponent<
+    (props: React.PropsWithChildren<ViewProps>) => React.ReactElement
+  >;
+  readonly defaultPath: string;
+  readonly appExtentions: {
+    savedObject: {
+      docTypes: [string];
+      toListItem: (obj: { id: string; title: string }) => ViewListItem;
+    };
+  };
+  readonly shouldShow?: (state: any) => boolean;
+}
+```
+
+---
 
-See the [OpenSearch Dashboards contributing
-guide](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/CONTRIBUTING.md) for instructions
-setting up your development environment.
+Original proposal: https://github.com/opensearch-project/OpenSearch-Dashboards/issues/4165