pypi_README.md: Add separate README for use in the pypi package #1456

Job	Run time
Merge tests 2 - Python () functional tests (Windows)	1m 18s
Merge tests 2 - Python (3.8) functional tests (Ubuntu)	43s
Merge test 1 - Twister (Windows) (mps2/an521/cpu0 - build only)	5m 58s
Merge tests 2 - Python (3.9) functional tests (Ubuntu)	44s
Merge test 1 - Twister (Ubuntu) (native_posix)	3m 48s
Merge tests 2 - Python (3.10) functional tests (Ubuntu)	41s
Merge test 1 - Twister (Ubuntu) (native_posix with asserts)	2m 56s
Merge tests 3 - Check repo files (Ubuntu)	20s
Merge tests 2 - Python (3.11) functional tests (Ubuntu)	41s
Merge test 1 - Twister (Ubuntu) (native_posix/native/64)	3m 17s
Merge tests 2 - Python (3.12) functional tests (Ubuntu)	46s
Merge test 1 - Twister (Ubuntu) (native_posix/native/64 with asserts)	2m 52s
Merge test 1 - Twister (Ubuntu) (mps2/an521/cpu0)	3m 41s
Merge test 1 - Twister (Ubuntu) (mps2/an521/cpu0 with asserts)	4m 0s
Release tests 3 (Python ${{ matrix.python-version }}${{ (((matrix.asserts != '') && ' with asserts') \|\| '') }})	0s
Release tests 1 - Check versions	0s
Release tests 4 (Python ${{ matrix.python-version }}${{ (((matrix.asserts != '') && ' with asserts') \|\| '') }})	0s
Release tests 2 - Fuzz	0s
	31m 45s

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