Fix latex in docstring

tests/test_scripts/test_solph/test_tsam/test_storage_tsam_integration.py

@@ -20,10 +20,10 @@
 An initial SOC of zero leads to infeasible solution, as last inter SOC has to
 match first inter SOC.
 Following equations have to be fulfilled:
-F_{el,st}[0] = F_{el,st}[6]
-SOC_{init} * discharge + F_{el,st}[0] =
-\sum_{i=1}^{n=5}F_{st,el}[i]/eff_{out}/(1 - discharge)^i
-F_{el,st}[6] = (SOC_{init} + F_{el,st}[5]/eff_{out}) / (1 - discharge)
+:math:`F_{el,st}[0] = F_{el,st}[6]`
+:math:`SOC_{init} * discharge + F_{el,st}[0] =`
+:math:`\sum_{i=1}^{n=5}F_{st,el}[i]/eff_{out}/(1 - discharge)^i`
+:math:`F_{el,st}[6] = (SOC_{init} + F_{el,st}[5]/eff_{out}) / (1 - discharge)`
 
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