Document iOS TDLib linking blocker

scripts/check-ios-tdlib-linking.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ -z "${DEVELOPER_DIR:-}" && -d /Applications/Xcode.app/Contents/Developer ]]; then
+  export DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer
+fi
+
+target="${IOS_RUST_TARGET:-aarch64-apple-ios-sim}"
+
+if ! rustup target list --installed | grep -qx "${target}"; then
+  rustup target add "${target}"
+fi
+
+cargo build -p tele-ios-ffi --target "${target}" --release