Update Readme.md

Author: Benjed

README.md

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 # CH3mculator
 A small tool to help you with stoichiometric calculations. Allows you to automatically get constant values of the compounds from [PubChem](https://pubchem.ncbi.nlm.nih.gov/).
 
+![Preview Image for the CH3mculator](https://github.com/Benjed/CH3mculator/blob/master/calculator_preview.png)
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 ## System Requirements ##
 - Windows operating system
 - .Net 5 Desktop Runtime