add contributing guidelines

Author: minaminao

CONTRIBUTING.md

@@ -0,0 +1,20 @@
+# Contributing Guidelines
+
+Thank you for your interest in contributing to this repository. While this is primarily a personal collection of CTF blockchain challenges and writeups, contributions are welcome! However, please note that I might modify files added by you as I see fit.
+
+## Contributions
+- **New Challenges**: Adding new CTF challenges from various competitions
+- **Solvers**: Adding new solutions or more efficient/interesting approaches to existing challenges
+- **Writeups**: Adding detailed explanations, solution walkthroughs, or improving existing documentation
+- **README Organization**: Improving categorization, descriptions, and fixing links
+
+## Repository Structure
+- Challenges are primarily organized by CTF in the [src/](src/) directory
+- Each CTF has its own subdirectory (e.g., [src/ParadigmCTF2022/](src/ParadigmCTF2022/), [src/Ethernaut/](src/Ethernaut/))
+- This repo use CI to check if challenges are solved through test files
+- When solving CTFs, I use scripts, and contracts that are commonly used by both tests and scripts are extracted (e.g., `Exploit.sol`)
+- Please refer to the [src/Templates/](src/Templates/) directory for examples of the expected structure
+
+---
+
+If you have questions about contributing, feel free to contact [@vinami](https://x.com/vinami) (due to many spam messages, my replies may be slow).

README.md

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 This repository collects blockchain challenges in CTFs and wargames.
 
 These challenges are categorized by topic, not by difficulty or recommendation.
-Also, there are my writeups and exploits for some challenges (e.g., [Paradigm CTF 2022](src/ParadigmCTF2022/)).
-Please be aware that these contain spoilers.
-
-If there are any incorrect descriptions, I would appreciate it if you could let me know via issue or PR!
+Some of them include writeups and solutions (e.g., [Paradigm CTF 2022](src/ParadigmCTF2022/)).
+Please be aware that these contain spoilers. For contribution guidelines, please see [CONTRIBUTING.md](CONTRIBUTING.md).
 
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