Added agents.md file

Author: Filter94

AGENTS.md

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+# Maru AGENTS.md file
+
+Maru is an Ethereum Consensus client that implements QBFT Consensus algorithm. It's meant to be used on Ethereum L2-s,
+the main focus is on Linea support. The main purpose or Maru is to enable the usage the existing Ethereum EL clients on
+Linea by setting the head of the chain with the Engine API. For that Maru maintains its own beacon chain, can peer with
+and sync from other Maru clients, same as other CL and EL Clients.
+
+## Code style and quality
+- Please use best practices from "Software Engineering at Google" book. Please aim to keep the code clean, readable and maintainable
+- When writing new classes, please stick to the OOP, SOLID principles and GOF Design Patterns
+- When adding a new file and the code, please refer to the existing files to write new code in a way that is uniform with the existing codebase
+- Kotlin is our main programming language. When writing new code, please avoid Java-like style and use Kotlin-native
+  idioms
+- Every time you're tempted to use inheritance, think again and use composition instead
+- Avoid in line comments. Use variable/function/class names and tests as a documentation. Note that javadocs near
+  classes and methods are fine in case they're really necessary
+- Please respect ktlint and .editorconfig rules
+
+## Dev environment tips
+- The whole project can be built by `make build` or simply `./gradlew build`. Note that it takes a few minutes to
+  run all the tests
+- Code can be formatted by `make spotless-happy` or `./gradlew spotlessApply`
+- When running the tests and debugging issues, please don't rely on console output, but rather parse the test
+  results html generated by Gradle directly
+
+## General instructions
+- Before considering the work complete, ALWAYS make sure:
+  - The whole project compiles
+  - The code is properly formatted