docs: add a page to help users get started with the EEST opcode minilang

[danceratopz]

There's only a very small section on "writing code for accounts"". We should add a page for test contributors that shows users:

1. How users to write smart contracts using the EEST Opcodes minilang (example driven):

   execution-spec-tests/src/ethereum_test_vm/opcode.py

   Line 403 in 851f9f5

   class Opcodes(Opcode, Enum):

2. Which higher-level constructs are available to help them do that (SwitchCase):

   execution-spec-tests/src/ethereum_test_tools/code/generators.py

   Line 303 in 851f9f5

   class Switch(Bytecode):

3. Points them to the evm_bytes CLI to automatically generate Opcode minilang from bytecode: https://eest.ethereum.org/main/library/cli/evm_bytes/

Related: #1779 forbids the use of Yul source in Python test cases.