docs(readme): add features and screenshots

Author: asqarslanov

README.md

@@ -1,5 +1,33 @@
 # EvOps / Back End
 
+Main repository: https://github.com/evops-sum25/evops
+
+## Features
+
+- API methods to create and view users, events, event images, and event tags
+  (groups).
+- Combined REST+gRPC web-server so that clients can choose their preferred
+  communication way.
+- Auto-generated OpenAPI documentation + Swagger webpage.
+- Persistent data storage with PostgreSQL.
+- Persistent image storage with MinIO.
+- Data validation at the type-system level.
+- Basic logging of incoming requests and their responses.
+- Configurability with environment variables and a [`.env`](/.env.example) file.
+- An [API extension](https://github.com/evops-sum25/evops-client-ext) for
+  clients to ease the interaction with our back end:
+  - Validation functions (such as `validate_event_title` or
+    `validate_tag_alias`) that reuse the logic from the back-end core.
+  - Fully-typed Markdown parser with our own parse settings.
+  - Exporting to WASM with Extism and Protobuf types.
+  - Generating type-safe FFI bindings with UniFFI.
+
+## Screenshots
+
+<img src="/assets/swagger-1.jpg" width=480 />
+<img src="/assets/swagger-2.jpg" width=480 />
+<img src="/assets/grpcui.jpg" width=480 />
+
 ## Build Instructions
 
 1. Create a [`.env`](`/.env.example`).