Add AT 14.0 to install documentation
Add AT 14.0 to install documentation

Added AT 14.0 to installation guide on the website.
Also, removed references to unsupported distros from the installation guide.

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