feat: Add CONVENTIONS.md file based on lib/vpc-functions

CONVENTIONS.md

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+# Coding Conventions
+
+This document outlines the coding conventions used in our project, particularly for bash scripts and AWS CLI commands.
+
+## Bash Scripts
+
+### Function Naming
+- Use lowercase with hyphens for function names (e.g., `vpc-subnets`, `vpc-route-tables`).
+- Function names should be descriptive of their purpose.
+
+### Comments
+- Use `#` for single-line comments.
+- Include a brief description of the function's purpose immediately after the function name.
+- For complex functions, add usage examples in the comments.
+
+### AWS CLI Commands
+- Use `aws` followed by the service name (e.g., `aws ec2`, `aws rds`).
+- Prefer `--output text` for consistent and easily parseable output.
+- Use `--query` with JMESPath expressions for filtering and formatting output.
+
+### Output Formatting
+- Use `columnise` (a custom function) to format output into columns.
+- Sort output when appropriate (e.g., `sort -k 5`).
+
+### Error Handling
+- Check for required arguments using `[[ -z "$vpc_ids" ]] && __bma_usage "vpc-id [vpc-id]" && return 1`.
+
+### Looping
+- Use `for` loops to iterate over multiple VPC IDs or other resources.
+
+### Variable Naming
+- Use lowercase for local variables (e.g., `local vpc_ids`, `local filters`).
+- Use uppercase for environment variables or constants (e.g., `$AWS_DEFAULT_REGION`).
+
+### Input Handling
+- Use `skim-stdin` (a custom function) to handle both piped input and arguments.
+
+## AWS Resource Naming
+- Use the format `resource-type-action` for function names that interact with specific AWS resources (e.g., `vpc-igw`, `vpc-nat-gateways`).
+
+## Output Conventions
+- For listing functions, output should typically include resource IDs and names.
+- Include 'NO_NAME' for resources without a Name tag.
+
+## Security Considerations
+- Be cautious with functions that perform destructive actions (e.g., `vpc-default-delete`).
+- Include safety checks before performing destructive actions.
+
+These conventions are derived from the observed patterns in the lib/vpc-functions file. They should be followed when contributing new functions or modifying existing ones to maintain consistency across the project.