docs: add Discord badge to README #363

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	37s
checks / test (3.11, lowest-direct, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	2m 53s
checks / test (3.10, lowest-direct, ubuntu-latest)	56s
checks / test (3.12, lowest-direct, windows-latest)	3m 32s
checks / test (3.13, lowest-direct, ubuntu-latest)	51s
checks / test (3.10, locked, windows-latest)	2m 52s
checks / test (3.13, locked, windows-latest)	2m 36s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.11, locked, ubuntu-latest)	47s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.13, lowest-direct, windows-latest)	2m 45s
checks / test (3.11, lowest-direct, windows-latest)	2m 51s
checks / test (3.13, locked, ubuntu-latest)	45s
checks / test (3.14, locked, windows-latest)	3m 53s
checks / test (3.14, lowest-direct, windows-latest)	2m 17s
checks / test (3.12, locked, windows-latest)	3m 37s
checks / test (3.11, locked, windows-latest)	2m 27s
checks / test (3.14, locked, ubuntu-latest)	2m 25s
checks / test (3.10, locked, ubuntu-latest)	51s
all-green	2s
	41m 10s

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