feat: adds contributing markdown (#75)

Closes #68

### Overview

Adds the CONTRIBUTING.md file to the repo. Includes a Quick Start guide
on how to set up the repo, install dependencies, and go through the rest
of the setup. Includes Development Guidelines with a link to the
STYLE_GUIDE.md

### Testing

_No testing_

### Screenshots / Screencasts

Preview of the markdown file (it's 3 pictures, sorry for the
formatting):
<img width="832" height="753" alt="contributing_1"
src="https://github.com/user-attachments/assets/748a16ae-2a29-46f5-941d-f0724128cc05"
/>
<img width="826" height="814" alt="contributing_2"
src="https://github.com/user-attachments/assets/1d951a42-739a-48a6-96b2-f613fecb8991"
/>
<img width="831" height="820" alt="contributing_3"
src="https://github.com/user-attachments/assets/e6526c74-ffe8-4ba1-882f-37a46c04898f"
/>


### Checklist
- [x] Code is neat, readable, and works
- [x] Code is commented where appropriate and well-documented
- [x] Commit messages follow our
[guidelines](https://www.conventionalcommits.com)
- [x] Issue number is linked
- [x] Branch is linked
- [ ] Reviewers are assigned (one of your tech leads)

Tip: You can make the issue and then check them after the fact or
replace `[ ]` with `[x]` to check it!

### Notes
Not sure if the STYLE_GUIDE.md is supposed to be incorporated into the
CONTRIBUTING.md file or if just linking it is sufficient. Also, much of
the content was taken from this repo's README.md and Cal Poly's H4I
repo, so let me know if something doesn't make sense or conform to
Operation's standards.

---------

Signed-off-by: Sophia Chang <[email protected]>
Co-authored-by: Sophia Chang <[email protected]>

Author: seanmnguyen

CONTRIBUTING.md

@@ -0,0 +1,111 @@
+# Contributing
+
+Here are all of the steps you should follow whenever contributing to this repo!
+
+---
+
+## Quick Start
+
+### 1. Setting Up the Repo
+
+1. Go to the project [repo](https://github.com/hack4impact/operations-api).
+2. Click the green "Code" button in the top right. Switch to the "HTTPS" tab.
+3. If you are using Github Desktop, click "Open with Github Desktop", otherwise click the "Copy URL to clipboard" button to the right of the URL.
+4. Go into your IDE/terminal and enter `git clone <paste-URL-here>`
+
+### 2. Install Dependencies
+
+```bash
+npm install
+```
+
+### 3. Environment Setup
+
+Create a `.env` file in the root directory and copy fields from `.env.example`:
+
+```env
+# Database Configuration
+DATABASE_URL=your_database_url_here
+DIRECT_URL=your_direct_url_here
+
+# Server Configuration
+PORT=3000
+REST_PORT=3001
+GRAPHQL_PORT=3002
+```
+
+Access the important fields from Vaultwarden from this: https://vault.hack4impact.org/#/login
+
+### 4. Database Setup
+
+```bash
+npx prisma db pull     # Sync schema with database
+npx prisma generate    # Generate Prisma client
+```
+
+### 5. Start Development Server
+
+```bash
+# Start integrated server (both REST & GraphQL)
+npm run dev
+
+# Or start servers separately
+npm run dev:rest       # REST API only
+npm run dev:graphql    # GraphQL API only
+npm run dev:both       # Both servers concurrently
+```
+
+The servers will be available at:
+
+- **Integrated**: <http://localhost:3001>
+- **REST API**: <http://localhost:3002>
+- **GraphQL API**: <http://localhost:3003>
+
+---
+
+## Development Guidelines
+
+_See Style Guide: [STYLE_GUIDE.md](https://github.com/hack4impact/operations-api/blob/main/STYLE_GUIDE.md)_
+
+### Branch Naming Convention
+
+Follow the pattern listed in your issue: `feature/issue-number-description`
+
+- Example: `feature/1-add-volunteer-endpoints`
+- This automatically links branches to GitHub issues
+- Create your branch off of the "develop" branch, not the main.
+
+### Making Changes
+
+1. Before you start making changes, always make sure you're on the develop branch, then `git pull` and `npm i` to make sure your code is up to date
+2. Create a branch `git checkout -b <name-of-branch>`
+3. Make changes to the code
+4. Run ESLint to ensure code standards (see in [style guide](https://github.com/hack4impact/operations-api/blob/main/STYLE_GUIDE.md#eslint)).
+
+### Committing Changes
+
+When interacting with Git/GitHub, feel free to use the command line, VSCode extension, or Github desktop. These steps assume you have already made a branch using `git checkout -b <branch-name>` and you have made all neccessary code changes for the provided task.
+
+1. View diffs of each file you changed using the VSCode Github extension (3rd icon on far left bar of VSCode) or GitHub Desktop
+2. `git add .` (to stage all files) or `git add <file-name>` (to stage specific file)
+3. `git commit -m "<type>[optional scope]: <description>"` or `git commit -m "<type>[optional scope]: <description>" -m "[optional body]"` or `git commit` to get a message prompt
+4. `git push -u origin <name-of-branch>`
+
+### Making Pull Requests
+
+1. Go to the Pull Requests tab on [github.com](https://github.com/)
+2. Find your PR, fill out the PR template
+3. (If applicable, provide a screenshot of your work in the comment area)
+4. Link your PR to the corresponding Issue
+5. Request a reviewer to check your code
+6. Once approved, your code is ready to be merged in 🎉
+
+### Testing
+
+```bash
+npm run test               # Run all tests (Unit &  Integration)
+npm run test:coverage      # Generate coverage report for Unit tests only
+npm run test:integration   # Integration tests only
+npm run test:unit          # Unit tests only
+npm run test:watch         # Watch mode for unit tests
+```