docs: warn about splitting geothermal central heating into two technologies in release notes

Author: amos-schledorn

docs/release_notes.rst

@@ -7,6 +7,8 @@ Release Notes
 
 * added water-sourced heat pumps based on upper uncertainty bounds from DEA technology catalogue ("40 Comp. hp, seawater 20 MW")
 
+* **WARNING**: Costs for central geothermal heating are split into `central geothermal heat source` and `central geothermal-sourced heat pump`. Make sure to use the costs of both for full systems!
+
 * added geothermal district heating as `central geothermal-sourced heat pump` and `central goethermal heat source` based on DEA technology catalogue ("45.1.a Geothermal DH, 1200m, E")
 
 * added Pyrolysis for biochar