docs: Move info from README to docs/

Signed-off-by: Tim Crawford <tcrawford@system76.com>

docs/building.md

@@ -0,0 +1,31 @@
+# Building
+
+Dependencies can be installed with the provided script.
+
+```
+./scripts/install-deps.sh
+```
+
+If rustup was installed for the first time, it will be required to source the
+environment file it installed to use the correct Rust toolchain.
+
+```
+. ~/.cargo/env
+```
+
+A script is provided to build the firmware. The available targets for building
+are the model folders in `models/`. For example, to build for QEMU:
+
+```
+./scripts/build.sh qemu
+```
+
+Once built, the firmware must be flashed to use. Several scripts are available
+to flash the new firmware, depending on how it is going to be written.
+
+- `scripts/qemu.sh`: [Run the firmware in QEMU](./debugging.md#using-qemu) (specific to the QEMU model)
+- `scripts/flash.sh`: Flash using firmware-update
+- `scripts/ch341a-flash.sh`: Flash using a CH341A programmer
+- `scripts/spipi-flash.sh`: Flash using a Raspberry Pi
+
+See [Flashing firmware](./flashing.md) for more details.