Added Dockerfile and building instructions

Dockerfile

@@ -0,0 +1,7 @@
+FROM rust:1.75.0-bullseye AS builder
+RUN apt-get update && apt-get -y upgrade && apt-get install -y make libclang-dev
+COPY . grandine
+RUN cd grandine && ./scripts/build/release.sh
+
+FROM ubuntu:latest
+COPY --from=builder /usr/local/cargo/bin/grandine /usr/local/bin/grandine

README.md

@@ -31,11 +31,57 @@ Then the build may take a few minutes:
 git clone https://github.com/grandinetech/grandine
 cd grandine
 git submodule update --init
-cargo build --release --features network-mainnet --features network-holesky --bin grandine
+cargo build --release --features default-networks
 ```
 
 The compiled binary is available at `./target/release/grandine`
 
+### Cross-compilation
+
+[Cross](https://github.com/cross-rs/cross) can be used for Grandine cross-compilation.
+
+Cross-compilation command for `amd64` architecture:
+
+```
+cross build \
+    --bin grandine \
+    --target x86_64-unknown-linux-gnu \
+    --features default-networks \
+    --profile release
+```
+
+Cross-compilation command for `arm64` architecture:
+
+```
+cross build \
+    --bin grandine \
+    --target aarch64-unknown-linux-gnu \
+    --features default-networks \
+    --profile release
+```
+
+### Docker builds
+
+Cross-compilated binaries can be used for Docker build images.
+
+Docker build command for `amd64` architecture:
+
+```
+docker build \
+    --file Dockerfile.cross \
+    --platform linux/amd64 \
+    ./target/x86_64-unknown-linux-gnu/release/
+```
+
+Docker buildx command for `arm64` architecture:
+
+```
+docker build \
+    --file Dockerfile.cross \
+    --platform linux/arm64 \
+    ./target/aarch64-unknown-linux-gnu/release/
+```
+
 ## Team
 
 Grandine is built by [Grandine core team](https://grandine.io/) led by [Saulius Grigaitis](https://twitter.com/sauliuseth).