Clarify in README that v0.9 and v1.0 are withdrawn

Update Readme:
- state that v1.0 is withdrawn
- set expectations for v2.0 release timeline

The version v.9 and v1.0 are withdrawn because products shipped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+Note that versions 0.9 and 1.0 of this specification are withdrawn and should not be used for product development.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/).
@@ -60,11 +62,8 @@ The U-Boot project hosts another library implementation, referred to as Bloblist
 Status
 ======
 
-The first release of the specification has been published. We are currently in
-the implementation phase, looking at various target projects, including U-Boot,
-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.
+As of November 2025, version 1.0 is withdrawn and should not be used.
+Version 1.0 was withdrawn because products shipped with a TL header cheksum implementation that differed from the version 1.0 definition.
 
-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.
+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.