Made changes to script

I renamed the file to reflect that it is only for MinGW (I plan to create
similar scripts for other operating systems), and added code to zip the release folder,
inside the shell script.

create_release_mingw.sh

@@ -19,3 +19,6 @@ cp "$BASE_DIR/build/pong" "$REL_DIR"
 # Remove the temporary file.
 rm "$BASE_DIR/tmp_file.txt"
 
+#Zip the $REL_DIR folder
+zip -r "$BASE_DIR/release/netpong-win.zip" "$REL_DIR"
+