All projects under the TrustedFirmware.org project now use the same
security incident process, therefore update the disclosure/vulnerability
reporting information in the TF-A documentation.

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/!\ IMPORTANT /!\

Please note that the email address to send these reports to has changed.
Please do *not* use trusted-firmware-security@arm.com anymore.

Similarly, the PGP key provided to encrypt emails to the security email
alias has changed as well. Please do *not* use the former one provided
in the TF-A source tree. It is recommended to remove it from your
keyring to avoid any mistake. Please use the new key provided on
TrustedFirmware.org from now on.
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Change-Id: I14eb61017ab99182f1c45d1e156b96d5764934c1
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>