implemented proper error handling, added README

README.md

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+# dev_tools
+
+CLI tool to start and stop a local RCC test environment. It manages a Docker Compose service and toggles environment variable files between local and CI database configurations.
+
+## Prerequisites
+
+- Rust toolchain (stable)
+- Docker with Compose plugin
+
+## Configuration
+
+The tool reads from a dotenv-style file at `~/.config/rcc/dev`. The following variables are required:
+
+| Variable | Description |
+|---|---|
+| `DOCKER_SERVICE` | Name of the Docker container to check if it is running |
+| `DOCKER_DIR` | Path to the Docker Compose directory, relative to `$HOME` |
+| `<PROJECT>_DIR` | Absolute path to the project directory (one per project, e.g. `FOO_DIR`) |
+
+Example `~/.config/rcc/dev`:
+```
+DOCKER_SERVICE=my-container
+DOCKER_DIR=repos/docker/local
+FOO_DIR=/home/user/repos/foo
+```
+
+## Build & Install
+
+```bash
+cargo build --release
+# or install directly into ~/.cargo/bin
+cargo install --path .
+```
+
+## Usage
+
+```
+dev_tools <project> <up|down> [--legacy]
+```
+
+| Argument | Description |
+|---|---|
+| `project` | Project key (matches `<PROJECT>_DIR` in the config, case-insensitive) |
+| `up` / `down` | Start or stop the environment |
+| `-l`, `--legacy` | Enable legacy mode: also toggles `conf/global/connections.env` and runs `git update-index` |
+
+### Examples
+
+```bash
+# Start the environment for project "foo"
+dev_tools foo up
+
+# Stop it
+dev_tools foo down
+
+# Start with legacy env handling
+dev_tools foo up --legacy
+```
+
+## What it does
+
+1. Starts or stops the Docker Compose service defined by `DOCKER_SERVICE` / `DOCKER_DIR`.
+2. Toggles database connection entries in `<PROJECT_DIR>/conf/local/.env` between `staging` and CI values.
+3. With `--legacy`: additionally modifies `conf/global/connections.env` and marks it with `git update-index --assume-unchanged` to avoid accidental commits.
+
+## Tests
+
+```bash
+cargo test
+```