an update of various things

docs/physics/thermodynamics/equilibrium-formalism.md

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+# Formalism of equilibrium thermodynamics
+
+Thermodynamics, the study of the behaviour of physical systems in terms of their macroscopic observables. A physical theory that perhaps is closest to our macroscopic perception of the physical world. 
+
+## References
+
+* A.M. Steane, *Thermodynamics*, Oxford University Press, 2017.
+* Dep. of Physics Oxford University, *Basics of Thermodynamics*.
+* D.A. Lavis and R. Frigg, *The Fundamentals of Thermodynamics*, Springer, 2025.