Explain why ca-certificates is required in the Dockerfile (#50)

* Explain why ca-certificates is required in the Dockerfile

The previous comment ("enables TLS/SSL for securely fetching dependencies")
implied this is generic Docker hygiene. That framing is misleading:
@livekit/rtc-node ships a native Rust core that reads the system trust store
via rustls-tls-native-roots, not Node's bundled CA roots. node:22-slim
doesn't ship /etc/ssl/certs/ca-certificates.crt, so without ca-certificates
Room.connect() fails with the misleading "failed to retrieve region info"
error.

Rewrite the comment to name the cause so a developer trimming the image
knows the line is load-bearing. No functional change.

* Tighten ca-certificates comment

* Restore TLS context and --no-install-recommends note; drop version-specific image name

Author: aryeila

Dockerfile

@@ -10,9 +10,10 @@ ENV PNPM_HOME="/pnpm"
 ENV PATH="$PNPM_HOME:$PATH"
 ENV HOME="/app"
 
-# Install required system packages and pnpm, then clean up the apt cache for a smaller image
-# ca-certificates: enables TLS/SSL for securely fetching dependencies and calling HTTPS services
-# --no-install-recommends keeps the image minimal
+# Install ca-certificates (the system CA bundle used for TLS), then clean
+# the apt cache. Required by the LiveKit SDK: the native Rust core reads
+# the system trust store at runtime, which the slim base image doesn't ship.
+# --no-install-recommends keeps the image minimal.
 RUN apt-get update -qq && apt-get install --no-install-recommends -y ca-certificates && rm -rf /var/lib/apt/lists/*
 
 # Pin pnpm version for reproducible builds