Remove private URL from documentation
Remove private URL from documentation

In the `README.txt` there is an URL pointing to an IBM's private network.
This patch removes it.

Fix #2108

Signed-off-by: Erwan Prioul <9949cc68615082c237e6af925cacbd2ea7f2e953@linux.ibm.com>

advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain,advancetoolchain/advance-toolchain