Add README.md with instruction on how to use this tool.

Signed-off-by: Afonso Oliveira <[email protected]>

Author: AFOliveira

ext/opcodes_maker/README.md

@@ -0,0 +1,89 @@
+# RISC-V Instruction Format Generator
+
+This tool converts RISC-V instruction YAML definitions into various output formats including C headers, Chisel, Rust, Go, and LaTeX documentation.
+
+## Prerequisites
+
+- Python 3
+- YAML Python package (`pip install pyyaml`)
+- Make
+
+## Directory Structure
+
+```
+.
+├── yaml_to_json.py    # Converts YAML instruction definitions to JSON
+├── generator.py       # Generates various output formats from JSON
+├── output/           # Generated files directory
+└── Makefile         # Build system configuration
+```
+
+## Input/Output Format
+
+### Input
+- YAML files containing RISC-V instruction definitions
+- Default input directory: `../../arch/inst`
+- Can be customized using `YAML_DIR` variable
+
+### Output
+All outputs are generated in the `output` directory:
+- `encoding.out.h` - C header definitions
+- `inst.chisel` - Chisel implementation
+- `inst.spinalhdl` - SpinalHDL implementation
+- `inst.sverilog` - SystemVerilog implementation
+- `inst.rs` - Rust implementation
+- `inst.go` - Go implementation
+- `instr-table.tex` - LaTeX instruction table
+- `priv-instr-table.tex` - LaTeX privileged instruction table
+- `instr_dict.json` - Intermediate JSON representation
+- `processed_instr_dict.json` - Final processed JSON
+
+## Usage
+
+### Basic Usage
+```bash
+make                        # Use default YAML directory
+make YAML_DIR=/custom/path  # Use custom YAML directory
+make clean                  # Remove all generated files
+make help                   # Show help message
+```
+
+### Pipeline Steps
+1. YAML to JSON conversion (`yaml_to_json.py`)
+   - Reads YAML instruction definitions
+   - Creates intermediate JSON representation
+
+2. Output Generation (`generator.py`)
+   - Takes JSON input
+   - Generates all output formats
+   - Places results in output directory
+
+### Customization
+- Input directory can be changed:
+  ```bash
+  make YAML_DIR=/path/to/yaml/files
+  ```
+- Default paths in Makefile:
+  ```makefile
+  YAML_DIR ?= ../../arch/inst
+  OPCODES_DIR := ../riscv-opcodes
+  OUTPUT_DIR := output
+  ```
+
+## Error Handling
+- Checks for required Python scripts before execution
+- Verifies input directory exists
+- Creates output directory if missing
+- Shows helpful error messages for missing files/directories
+
+## Cleaning Up
+```bash
+make clean  # Removes all generated files and output directory
+```
+
+## Dependencies
+- Requires access to RISC-V opcodes repository (expected at `../riscv-opcodes`)
+- Python scripts use standard libraries plus PyYAML
+
+## Note
+Make sure your input YAML files follow the expected RISC-V instruction definition format. For format details, refer to the RISC-V specification or example YAML files in the arch/inst directory.