docs: added a developer.md file (#19)

* docs: add a developer.md file

* fix

* fix devmd

* better

* fix package name

Author: twishabansal

packages/toolbox-core/DEVELOPER.md

@@ -0,0 +1,102 @@
+# Development
+
+This guide provides instructions for setting up your development environment to contribute to the `@toolbox/core` package, which is part of the `mcp-toolbox-sdk-js` monorepo.
+
+## Prerequisites
+
+Before you begin, ensure you have the following installed:
+
+* Node.js ([LTS version recommended](https://nodejs.org/en/download/))
+
+## Setup
+
+These steps will guide you through setting up the monorepo and this specific package for development.
+
+1. Clone the repository:
+
+    ```bash
+    git clone https://github.com/googleapis/mcp-toolbox-sdk-js.git
+    ```
+
+2. Navigate to the **package directory**:
+
+    ```bash
+    cd mcp-toolbox-sdk-js/packages/toolbox-core
+    ```
+
+3. Install dependencies for your package:
+
+    ```bash
+    npm install
+    ```
+
+4. Local Testing
+    If you need to test changes in `@toolbox/core` against another local project
+    or another package that consumes `@toolbox/core`, you can use npm link
+
+    * In packages/toolbox-core
+
+        ```bash
+        npm link
+        ```
+
+    * In your consuming project
+
+        ```bash
+        npm link @toolbox/core
+        ```  
+
+    This creates a symbolic link, allowing changes in `@toolbox/core` to be
+    immediately reflected in the consuming project without reinstallation.
+
+    Don't forget to npm unlink / yarn unlink when done!
+
+## Testing
+
+Ensure all tests pass before submitting your changes. Tests are typically run from within the `packages/toolbox-core` directory.
+
+> [!IMPORTANT]
+> Dependencies (including testing tools) should have been installed during the initial `npm install` at the monorepo root.
+
+1. **Run Unit Tests:**
+
+    ```bash
+    npm run test:unit
+    ```
+
+1. **Run End-to-End (E2E) / Integration Tests:**
+
+    ```bash
+    npm run test:e2e
+    ```
+
+## Linting and Formatting
+
+This project uses linters (e.g., ESLint) and formatters (e.g., Prettier) to maintain code quality and consistency.
+
+1. **Run Linter:**
+    Check your code for linting errors:
+
+    ```bash
+    npm run lint
+    ```
+
+2. **Fix Lint/Format Issues:**
+    Automatically fix fixable linting and formatting issues:
+
+    ```bash
+    npm run fix
+    ```
+
+## Committing Changes
+
+* **Branching:** Create a new branch for your feature or bug fix (e.g., `feature/my-new-feature` or `fix/issue-123`).
+* **Commit Messages:** Follow [Conventional Commits](https://www.conventionalcommits.org/en/v1.0.0/) for commit message conventions.
+* **Pre-submit checks:** On any PRs, presubmit checks like linters, unit tests
+  and integration tests etc. are run. Make sure all checks are green before
+  proceeding.
+* **Submitting a PR:** On approval by a repo maintainer, *Squash and Merge* your PR.
+
+## Further Information
+
+* If you encounter issues or have questions, please open an [issue](https://github.com/googleapis/mcp-toolbox-sdk-js/issues) on the GitHub repository.