docs(examples): add tutorial-style README for leios-testnet (#790) #67

Job	Run time
Isolated no-default-features	37s
Features (--no-default-features)	1m 7s
Rustfmt	13s
Clippy	1m 20s
Docs	1m 10s
Test (windows-latest)	8m 49s
MSRV (1.88)	35s
Features (--all-features)	1m 22s
Test (macos-latest)	6m 57s
Test (ubuntu-latest)	5m 6s
	27m 16s

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