Rework README

Previews

• GitHub https://github.com/postgres-ai/database-lab-engine/blob/rework-readme/README.md
• GitLab https://gitlab.com/postgres-ai/database-lab/-/blob/rework-readme/README.md

Changes

• Added CODE_OF_CONDUCT.md
• Added CONTRIBUTING.md
• Added SECURITY.md
• Changed logo graphics (wide logo, new font, Cuprum)
• New section: Features
• Animated GIF demonstrating fast cloning of 1 TiB database
• Balance between GitHub and GitLab (the latter is supposed to be source of truth for the code, but both are fine for communicating with community)
• "Powered by" graphics for dark and light backgrounds
• Brief license description
• More words about Community throughout the texts

TODO

• MR desc
• proofread
• polish graphics
• badges

README.md

@@ -8,7 +8,7 @@ Database Lab Engine (DLE) is an open source technology that allows blazing-fast
 
 - Build dev/QA/staging environments based on full-size production-like databases.
 - Provide temporary full-size database clones for SQL query analysis and optimization (see also: [SQL optimization chatbot Joe](https://gitlab.com/postgres-ai/joe)).
-- Automatically verify database migrations (DB schema changes) and massive data changes in CI/CD pipelines to minimize the risks of downtime and performance degradation.
+- Automatically test database changes in CI/CD pipelines to avoid incidents in production.
 
 For example, cloning a 10 TiB PostgreSQL database can take less than 2 seconds and dozens of such clones can run on a single machine without extra costs, supporting many development and testing activities.