Move some documentation to docs/ and start overhaul

docs/development/cross-compilation.md

@@ -0,0 +1,13 @@
+# Cross compilation
+
+Install docker:
+
+```bash
+sudo apt install docker
+sudo usermod -aG docker $USER
+exec sudo su -l $USER
+sudo systemctl start docker
+cargo install cross
+cross build --release --target armv7-unknown-linux-musleabihf
+```
+The cross-compiled binary is at target/armv7-unknown-linux-musleabihf/release/conduit