docs: updated the README.

README.md

@@ -7,14 +7,42 @@ covers so much area that most of the video was of blue sky.
 PiPoint solves this problem by automatically pointing a ground based
 camera at the rover using GPS, a telemtry link, and pan/tilt unit.
 
+## Implementation
+
+![Overview](overview.svg)
+
+The system consists of:
+
+On the rover:
+
+* a [PixFalcon Micro](https://hobbyking.com/en_us/pixfalcon-micro-px4-autopilot-plus-micro-m8n-gps-and-mega-pbd-power-module.html)
+* GPS
+* [SiK radio](https://hobbyking.com/en_us/hkpilot-transceiver-telemetry-radio-set-v2-433mhz.html)
+  for telemetry
+
+In the base station:
+
+* a [Rasperry Pi 3](https://www.raspberrypi.org/products/raspberry-pi-3-model-b/)
+* SiK radio for telemetry
+* a [Lynx B servo based pan and tilt kit](http://www.lynxmotion.com/p-287-lynx-b-pan-and-tilt-kit-black-anodized.aspx)
+* a [Turnigy 2K HD actioncam](https://hobbyking.com/en_us/turnigy-2k-hd-camera-black-edition-lite-package.html)
+* A laser cut camera adaptor
+* A extra wifi USB adapter for the home network
+* A Linux laptop for display and control
+
+Assembling this is left as an exercise for the reader :)  There are some
+photos on [my blog](https://juju.net.nz/michaelh/blog/).
+
 ## Build
 
+* See `hardware/` and
+  [https://www.tinkercad.com/dashboard/search?q=pipoint](Tinkercad)
+  for the camera adapter.
 * See `ansible/` for rules to set up the Raspberry Pi.
-* See `etc/` for files used on the PX4 or Raspberry Pi.
+* See `etc/` for files used on the PX4 or Raspberry Pi.  Copy
+  `extra.txt` to `etc/extra.txt` on the PixFalcon SD card.
 * See `Makefile` for shortcuts to build pipoint itself.
 
-More instructions to come!
-
 # Note
 This is not an official Google product.