doc: Keypair constructors #1584

Job	Run time
Docs - stable toolchain (recent)	11s
Test - 1.63.0 toolchain (minimal)	5m 45s
Test - 1.63.0 toolchain (recent)	5m 41s
Prepare	3s
Test 32-bit version	26s
Format - nightly toolchain	11s
Test - stable toolchain (minimal)	3m 5s
Test - stable toolchain (recent)	3m 17s
WASM - stable toolchain	1m 35s
no-std - nightly toolchain (recent)	55s
Bench - nightly toolchain (recent)	19s
ASAN - nightly toolchain (recent)	1m 39s
Docs - nightly toolchain (recent)	21s
Lint - nightly toolchain (recent)	30s
Test - nightly toolchain (minimal)	2m 42s
Test - nightly toolchain (recent)	2m 32s
	29m 12s

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