update readme with build command

Author: Robert-Morgowicz

README.md

@@ -1,2 +1,6 @@
 # charasort_py
 An open source adversarial user-input character sorter.  It is designed to use arbitrary user images as source input.  Built on python3. This project was inspired by the web-based Touhou Project Character sorter: https://github.com/execfera/charasort/
+
+# build process
+For a fully-packaged executable:
+pyinstaller -p charasort charasort\charasort.py