WIP started on Board Support Crate docs

down-the-stack-book/src/supporting_your_particular_board.md

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 # Supporting your particular board
+
+---
+
+## Using a 'normal' PC
+
+* Did you tell your PC it had a mouse plugged in?
+* Did you tell it what I/O address the video card was located at?
+* No! It auto-discovers all of these things.
+  * USB, PCI-Express, SATA all have "plug-and-play"
+
+---
+
+## Using an Embedded System
+
+* There is no plug-and-play
+* Your MCU can put different functions (UART, SPI, etc) on different pins
+* The choice of which function goes on which pin was decided by the PCB designer
+* You now have to tell the software how the PCB was laid out
+  * i.e UART0 TX is on Port 0, Pin 13
+
+---
+
+## Board Support Crates
+
+* You can wrap this up into a Board Support Crate
+* Especially useful if you are using a widely available dev-kit
+  * e.g. the nRF52840-DK, or the STM32 Discovery
+* Still useful if the board design is an in-house one-off
+* Create the drivers and does the pin assignments for you
+* Helps make your application portable across different boards
+
+---
+
+## Using a Board Support Crate
+
+```rust
+
+```
+
+---