Fix bios boot python script due to 1.8.x changes

[iamveritas]

Change Description

1. Adds PREACTIVATE_FEATURE before eosio.system.
2. Adds the rest of the features that could be activated if user wants to.
3. Update README.md file.

Resolves #8261

• Documentation Updates

[heifner]

Note release/2.0.x will add two more: WEBAUTHN_KEY & WTMSIG_BLOCK_SIGNATURES

info  2019-12-10T14:18:03.212 thread-0  chain_plugin.cpp:410          operator()           ] Support for builtin protocol feature 'WTMSIG_BLOCK_SIGNATURES' (with digest of '299dcb6af692324b899b39f16d5a530a33062804e41f09dc97e9f156b4476707') is enabled with preactivation required
info  2019-12-10T14:18:03.212 thread-0  chain_plugin.cpp:520          operator()           ] Saved default specification for builtin protocol feature 'WTMSIG_BLOCK_SIGNATURES' (with digest of '299dcb6af692324b899b39f16d5a530a33062804e41f09dc97e9f156b4476707') to: /Users/heifner/ext/eosio/build/programs/nodeos/c/protocol_features/BUILTIN-WTMSIG_BLOCK_SIGNATURES.json
info  2019-12-10T14:18:03.212 thread-0  chain_plugin.cpp:410          operator()           ] Support for builtin protocol feature 'WEBAUTHN_KEY' (with digest of '4fca8bd82bbd181e714e283f83e1b45d95ca5af40fb89ad3977b653c448f78c2') is enabled with preactivation required
info  2019-12-10T14:18:03.213 thread-0  chain_plugin.cpp:520          operator()           ] Saved default specification for builtin protocol feature 'WEBAUTHN_KEY' (with digest of '4fca8bd82bbd181e714e283f83e1b45d95ca5af40fb89ad3977b653c448f78c2') to: /Users/heifner/ext/eosio/build/programs/nodeos/c/protocol_features/BUILTIN-WEBAUTHN_KEY.json