Move bootloader main to examples

This should remove some confusion around embassy-boot-* being a library
vs. a binary. The binary is now an example bootloader instead.

examples/boot/application/nrf/README.md

@@ -0,0 +1,34 @@
+# Examples using bootloader
+
+Example for nRF52 demonstrating the bootloader. The example consists of application binaries, 'a'
+which allows you to press a button to start the DFU process, and 'b' which is the updated
+application.
+
+
+## Prerequisites
+
+* `cargo-binutils`
+* `cargo-flash`
+* `embassy-boot-nrf`
+
+## Usage
+
+
+
+```
+# Use bare metal linker script
+cp memory-bl.x ../../bootloader/nrf/memory.x
+
+# Flash bootloader
+cargo flash --manifest-path ../../bootloader/nrf/Cargo.toml --features embassy-nrf/nrf52840 --release --chip nRF52840_xxAA
+# Build 'b'
+cargo build --release --bin b
+# Generate binary for 'b'
+cargo objcopy --release --bin b -- -O binary b.bin
+```
+
+# Flash `a` (which includes b.bin)
+
+```
+cargo flash --release --bin a --chip nRF52840_xxAA
+```