Add README with some info on the flowHEADmaster

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+The fundamental design is that all the controls set flow variables.
+
+The variables are used in the main logic function consolidated export control, because (almost) everything boils down to how much are we importing or exporting right now - i.e what is the grid setpoint.
+
+The flow supports DC coupled PV and AC coupled PV, with a meter on the AC coupled inverter. I have an older version that works when there is no AC meter (by estimating the AC PV relative to the measured DC PV).
+
+You can:
+
+    set a scheduled import during the cheap time at a specified power level, stopping when specified SOC is reached
+    set a scheduled export during the expensive time at a specified power level, stopping when specified SOC is reached
+    enable/disable grid export of any excess power when the battery is full (SOC level that counts as full is specifieable)
+    export during daytime to be a specified fraction of current generation
+    set immersion heater on/off (actually the cerbo relay1)
+
+Status info is shown for current SOC, current total generation, current charge rate, how many kWh till full, how long it will be till the battery is full (or that it is currently discharging) , current home consumption. AC and DC generation separately, time.
+
+There is a solar forecast section in there but I failed to get that to work so far (I get API errors) so either ignore (or fix) that part.
+
+The controls are:
+Import:
+
+    Import now to force import right now at the power level on the input power slider.
+    Enable scheduled causes import at the power level on the input power slider between 2am and 5am (flux tarrif hard-coded), until Max import charge SOC is reached then stop. (one day max import charge SOC will be set by the solar forecast, but currently its manual)
+    Import Power sets the import power level used by the above controls. It goes up to 10kW but my inverter/charger is actually limited to 3.6kW. The system self-limits if you set it too high. The headroom is useful during free electricity hours so you can set inverter to full-power import/charge even when it is sunny.
+
+Export
+
+    Export now to force export right now at the power level on the export power slider.
+    Enable scheduled causes import at the power level on the input power slider between 4pm and 7pm (flux tarrif hard-coded), until Max import charge SOC is reached then stop
+    Auto Export when full. If enabled, export any generation above current consumption once battery reaches set SOC (Battery Full Level). If not enabled system will keep charging until 100% SOC before exporting.
+    Export PV% set export to be configurable fraction (PV export fraction) of current generation (between 7am and 4pm)
+    There is code for an enable battery balancing knob too, which adds 250W to the current import. The idea is that it provides some current to top off the pack for balancing, but at least on my system it doesnt because once the battery sets CCL (charge current limit) to 0, charging current is entirely inhibited.
+    Current setpoint shows what import (positive values) or export (negative values) is being asked for
+    Actual grid power (import +ve) shows what import/export is actually occuring right now. This should be similar to Current setpoint, but there are circumstances when it will differ, and it will take a few seconds to change after the setpoint changes.
+    Battery Full level set SOC% used by Auto export when full to control what level charging stops at (and excess generation is exported instead).
+    Min discharge SOC sets level at which scheduled discharge stops discharging, to ensure enough battery to run on overnight.
+
+Status
+
+    SOC %: Current state of charge
+    Total PV (W): Sum of current AC and DC-coupled generation
+    Battery charge rate: Current rate of battery charge (+ve) or discharge (-ve)
+    kWh to full: How many kWh until battery is full. Change batt size in Time till Full function (and convert to kWh unfilled node).
+    Time till full: How many hours until battery will be full (when charging). When discharging it says Discharging.
+    Consumption (W): current household power consumption.
+    AC PV Power (Fronius): Current AC-coupled PV generation
+    DC PV Power (Victron): Current DC-coupled PV generation
+    Time self-explanatory
+    Hot water immersion: state of Cerbo relay1
+
+Notes
+
+This code has not really been designed for external use. The design is moderately clean, but some things are currently hard-coded: such as battery size and flux tariff times. It wouldnt take much work to make it more generalised. Patches welcome.
+
+There is a 2nd copy of the consolidated export control node. This is so that you can be using one version and messing with another. Its then easy to connect up the new one for testing, but still have the old, known-working version to go back to quickly. This is very handy when working with a live system as its easy to write code which does the wrong thing!
+
+There are various settings in consolidated export control such as DNO export limit, and zerosetpoint which you might want to change. zerosetpoint is -30W so the system reliably avoids importing power.
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