docs: add contributions docs for llms and humans

Author: AlbertoCentonze

CLAUDE.md

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+- When adding or modifying a command in the CLI, the .toml config file should be updated as well.
+- Every time there is a user facing change the @docs/ should be updated according to @docs/CONTRIBUTING.md
+- When making a new rule you need to assign "NTX<seq>" code, always use the highest seq value that has yet not been used.

docs/CONTRIBUTING.md

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+# Documentation Contribution Guidelines
+
+## Adding New Rule Documentation
+
+1. Create a new file in `docs/rules/<rule-name>.md`
+2. Use this template:
+
+```markdown
+# Rule Name
+
+| Property | Value |
+|----------|-------|
+| Rule Code | `NTXN` |
+| Severity | Warning/Style/Optimization/Important |
+| Configuration | `param_name` - Description (default: value) |
+
+## Background
+Brief explanation of why this rule exists.
+
+## Purpose
+What the rule detects or enforces.
+
+## Example
+```vyper
+# Non-compliant code
+...
+
+# Compliant code
+...
+```
+
+## Configuration
+### pyproject.toml
+```toml
+[tool.natrix.rule_configs.RuleName]
+param = "value"
+```
+
+### Command Line
+```bash
+natrix --rule-config RuleName.param=value
+```
+```
+
+3. **Important**: 
+   - Only include the Configuration section if the rule has configurable parameters
+   - Do not add arbitrary sections - stick to the template
+   - Keep the structure consistent with existing rule documentation
+
+4. Update `docs/rules/index.md` with the new rule entry
+
+5. Add the rule to `mkdocs.yml` navigation:
+   ```yaml
+   nav:
+     - Rules:
+       - Rule Name (NTXN): rules/rule-name.md
+   ```
+
+6. Update `docs/configuration.md` if the rule has configurable parameters
+
+7. Verify the documentation builds correctly:
+   ```bash
+   mkdocs build
+   ```