[BUGFIX] Wrong cmd example in INSTALL.txt

The INSTALL.txt file has an example on how to create a link
in Windows using the MKLINK command.

Unfortunately the parameters in the example have the wrong order.

Resolves: #46119
Releases: 6.1, 6.0, 4.7, 4.5
Change-Id: Ida960d79e0144c15afdd7c21a9cd35466ec24545
Reviewed-on: https://review.typo3.org/18808
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn