Promote the v2 README to README.md ahead of the first v2 beta #3157

Job	Run time
checks / readme-snippets	15s
checks / docs	36s
checks / pre-commit	1m 5s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 13s
checks / test (3.10, lowest-direct, windows-latest)	1m 43s
checks / test (3.11, locked, windows-latest)	1m 47s
checks / test (3.13, lowest-direct, windows-latest)	1m 51s
checks / test (3.12, locked, ubuntu-latest)	1m 30s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 10s
checks / test (3.14, locked, ubuntu-latest)	2m 12s
checks / test (3.12, locked, windows-latest)	1m 38s
checks / test (3.14, lowest-direct, windows-latest)	1m 22s
checks / test (3.14, locked, windows-latest)	2m 31s
checks / test (3.13, locked, windows-latest)	1m 33s
checks / test (3.11, locked, ubuntu-latest)	1m 7s
checks / test (3.10, locked, ubuntu-latest)	1m 13s
checks / test (3.11, lowest-direct, windows-latest)	1m 42s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.13, locked, ubuntu-latest)	1m 6s
checks / test (3.10, locked, windows-latest)	1m 40s
checks / test (3.12, lowest-direct, windows-latest)	1m 38s
all-green	2s
	32m 43s

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