docs: Add a basic security document

Based loosely on the Linux kernel
Documentation/admin-guide/security-bugs.rst file, create a basic
security document for U-Boot.  In sum, security issues should be
disclosed in public on the mailing list if at all possible as an initial
position.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

doc/develop/index.rst

@@ -14,8 +14,9 @@ General
    patman
    process
    release_cycle
-   system_configuration
+   security
    sending_patches
+   system_configuration
 
 Implementation
 --------------

doc/develop/security.rst

@@ -0,0 +1,32 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+Handling of security vulnerabilities
+====================================
+
+The U-Boot project takes security very seriously.  As such, we'd like to know
+when a security bug is found so that it can be fixed and disclosed as quickly
+as possible.
+
+Contact
+-------
+
+The preferred initial point of contact is to send email to
+`u-boot@lists.denx.de` and use `scripts/get_maintainers.pl` to also include any
+relevant custodians. In addition, Tom Rini should be contacted at
+`trini@konsulko.com`.
+
+CVE assignment
+--------------
+
+The U-Boot project cannot directly assign CVEs, nor do we require them for
+reports or fixes, as this can needlessly complicate the process and may delay
+the bug handling. If a reporter wishes to have a CVE identifier assigned ahead
+of public disclosure, they will need to coordinate this on their own.  When
+such a CVE identifier is known before a patch is provided, it is desirable to
+mention it in the commit message if the reporter agrees.
+
+Non-disclosure agreements
+-------------------------
+
+The U-Boot project is not a formal body and therefore unable to enter any
+non-disclosure agreements.