Replace emoji with plain text in architecture diagrams and add text language hint

Author: dash14

README.md

@@ -22,7 +22,7 @@ buildcage solves this by restricting outbound network access during builds to on
 
 buildcage runs as a [remote driver](https://docs.docker.com/build/builders/drivers/remote/) for Docker Buildx. All `RUN` step containers are placed on an isolated network, and outbound traffic is routed through a proxy that enforces your allowlist.
 
-```
+```text
 ┌─ Docker Buildx (remote driver) ───────────────────────────┐
 │                                                           │
 │  buildcage container                                      │
@@ -34,8 +34,8 @@ buildcage runs as a [remote driver](https://docs.docker.com/build/builders/drive
 │  │  │ RUN step        │───→│ Proxy (nginx)         │   │  │
 │  │  │ (isolated net)  │    │                       │   │  │
 │  │  │ npm install,    │    │ allowed domain?       │   │  │
-│  │  │ apt-get, etc.   │    │  ✅ → internet        │   │  │
-│  │  └─────────────────┘    │  ❌ → blocked + logged│   │  │
+│  │  │ apt-get, etc.   │    │  Yes → internet       │   │  │
+│  │  └─────────────────┘    │  No  → blocked+logged │   │  │
 │  │                         └───────────────────────┘   │  │
 │  └─────────────────────────────────────────────────────┘  │
 └───────────────────────────────────────────────────────────┘
@@ -332,7 +332,7 @@ buildcage creates a controlled network environment for your Docker builds:
 
 ### Architecture Diagram
 
-```
+```text
 ┌──────────────────────────────────────────────────────────────────┐
 │ Builder container (privileged, single container)                 │
 │                                                                  │