Write a Windows PowerShell script that will perform the following functions:
- Search your computer for files ending with a .doc, .docx, .xls, or .xlsx file extension.
- Output the filenames and sizes (in groups by file extension) to a text file named â€œFile_Summary.txtâ€. The output should also conclude with a total of the number of files and total file size for each file extension.
- Include comments in the script code to document the functionality of the script.