In the top-level README.md, add an explanation of what this fork adds
compared to the upstream Arm-2D repository.

Remove information regarding releases and "main" and "developing"
branches, which are for the upstream repository and not applicable to
this fork.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>

This demonstrates how a user creates a CMake project that
* gets Arm-2D and its dependencies using the Open IoT SDK
* creates applications that use and link against Arm-2D
* gets platform support from an MCU-Driver-HAL implementation, in this
case mcu-driver-reference-platforms-for-arm.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>

* improve support for linux

* introduce arm_2d_helper_pfb_flush() to pfb helper.

* Update README.md

* update arm_2d_helper_is_time_out()

* fix template projects