feat: use rustembedded/cross images and use static relocation model to fix cross-compile

cross/README.md

@@ -0,0 +1,37 @@
+## Cross compilation
+
+The `cross` folder contains a set of convenience scripts (`build.sh` and `test.sh`) for cross-compiling Conduit.
+
+Currently supported targets are
+
+- aarch64-unknown-linux-musl
+- arm-unknown-linux-musleabihf
+- armv7-unknown-linux-musleabihf
+- x86\_64-unknown-linux-musl
+
+### Install prerequisites
+#### Docker
+[Installation guide](https://docs.docker.com/get-docker/).
+```sh
+$ sudo apt install docker
+$ sudo systemctl start docker
+$ sudo usermod -aG docker $USER
+$ newgrp docker
+```
+
+#### Cross
+[Installation guide](https://github.com/rust-embedded/cross/#installation).
+```sh
+$ cargo install cross
+```
+
+### Buiding Conduit
+```sh
+$ TARGET=armv7-unknown-linux-musleabihf ./cross/build.sh --release
+```
+The cross-compiled binary is at `target/armv7-unknown-linux-musleabihf/release/conduit`
+
+### Testing Conduit
+```sh
+$ TARGET=armv7-unknown-linux-musleabihf ./cross/test.sh --release
+```