Added powershell notes to the knowledge base

knowledge base/powershell.md

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+# Windows PowerShell
+
+## TL;DR
+
+```powershell
+# print the value of the PATH environment variable
+Write-Output $env:PATH
+
+# calculate the hash of a file
+CertUtil -hashfile path/to/file sha256
+
+# get super user privileges
+powershell Start-Process powershell -Verb runAs
+```
+
+## Further readings
+
+- [How to print environment variables to the console in PowerShell?]
+- [Running PowerShell as Administrator with the Command Line]
+
+[how to print environment variables to the console in powershell?]: https://stackoverflow.com/questions/50861082/how-to-print-environment-variables-to-the-console-in-powershell#50861113
+[running powershell as administrator with the command line]: https://adamtheautomator.com/powershell-run-as-administrator/