Added version 2021.2

docs/2020.4.1/example.md

docs/2020.4.1/install-core.md

docs/2020.4.1/install-modules.md

docs/2020.4.1/installation.md

docs/2020.4.1/interfaces.md

docs/2020.4.1/logging.md

docs/2020.4.1/modules/mod_hydra.md

docs/2020.4.1/modules/mod_medusa.md

docs/2020.4.1/modules/mod_nmap.md

docs/2020.4.1/modules/mod_test.md

docs/2020.4.1/plan-execution.md

docs/2020.4.1/stage-execution.md

docs/2020.4.1/step-execution.md

docs/2021.2.1/advanced-example.md

docs/2021.2.1/architecture.md

docs/2021.2.1/attack-modules.md

docs/2021.2.1/basic-example.md

docs/2021.2.1/cli.md

docs/2021.2.1/execution.md

docs/2021.2.1/howto-create-attack-modules.md