Clarify in README that v0.9 and v1.0 are withdrawn

The version v.9 and v1.0 are withdrawn because products shipped
with a TL header checksum implementation that differed from what was
spec'd (implementations used sum-based checksum, whereas spec mandated
xor).

Change-Id: Ibff46e7d88fcec0b1f3352aa7cebd7f5a7204e47
Signed-off-by: Jose Marinho <jose.marinho@arm.com>

Author: jmarinho

README.md

@@ -6,6 +6,8 @@ This repository contains the Firmware Handoff specification, which defines a
 data structure to transfer essential configuration information between firmware
 stages during platform initialization.
 
+Note that versions 0.9 and 1.0 of this specification are withdrawn and should not be used for product development.
+
 The documentation is generated using the Sphinx framework. A version of this
 specification, rendered in HTML, is available
 [here](https://firmwarehandoff.github.io/firmware_handoff/).
@@ -53,5 +55,8 @@ coreboot, TF-A and Tianocore. Once this is done we will review the result to see
 if any serious flaws have come to light, meaning that changes are needed.  If
 so, these will be undertaken in each project.
 
-By the end of 2024, the spec will be considered stable and will be published
-as version 1. From there on, backwards compatibility will be maintained.
+As of November 2025, version 1.0 is withdrawn and should not be used.
+Version 1.0 was withdrawn because products shipped with an TL header cheksum implementation that differed from the version 1.0 definition.
+
+A version 2.0 of the specification is currently under work and will be published shortly.
+Implementations should adopt version 2.0 of the specification.