put some content into the README

README.md

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 # hortitel
-Allotment Telemetry Project: horti(culture)tel(emetry)
+Allotment Telemetry Project: Horti(culture)Tel(emetry)
+
+Project Goal: Gather various sensor data from our allotment so we can observe present data and compare to past measurements.
+
+This is initially using the Melopero Perpetuo LoRa boards as documented in their project here:
+
+The code is derived from their initial examples.
+
+At present this reads some data from the 'sender' board and sends it via the
+LoRaEMB protocol to the 'receiver board. The data sent is the Pico's internal
+temperature sensor as well as voltage readings from the battery circuit and the
+board input voltage (i.e. USB or solar). Note that the voltage measurement uses
+an external voltage divider circuit, the resistances of this are essentially
+documented in the code.
+
+The data is sent and received by serialisation and deserialisation of some
+structs.  It could well be neater to use a text format for, but I'm a bit
+old-school like this.
+
+Eventually I plan to build this out by adding more sensors, a proper enclosure,
+and an external solar/battery power-source.
+
+The code is in no way warranted to be fit for any purpose at all. In fact it is
+almost certainly "buggy as hell". You have been warned.