feat: initial module 3

module-03-branching/README.md

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+# Module 03: Branching Basics
+
+## Learning Objectives
+
+In this module, you will:
+- Understand what a branch is in Git
+- Create new branches using `git branch` or `git checkout -b`
+- Switch between branches using `git checkout` or `git switch`
+- View all branches with `git branch`
+- Understand that branches allow parallel development
+
+## Challenge
+
+### Setup
+
+Run the setup script to create your challenge environment:
+
+```powershell
+.\setup.ps1
+```
+
+This will create a `challenge/` directory with a Git repository that has some initial commits on the main branch.
+
+### Your Task
+
+Your goal is to create a feature branch, make commits on it, and understand how branches work independently.
+
+**Steps:**
+
+1. Create a new branch called `feature-login`
+2. Switch to the new branch
+3. Create a new file `login.py` with some login functionality
+4. Commit the new file to your feature branch
+5. Make another change to `login.py` and commit it
+6. Switch back to the main branch and observe that `login.py` doesn't exist there
+
+**Suggested Approach:**
+
+1. Navigate to the challenge directory: `cd challenge`
+2. View existing branches: `git branch`
+3. Create and switch to new branch: `git checkout -b feature-login`
+4. Create `login.py` with any content you like
+5. Stage and commit: `git add login.py` and `git commit -m "Add login functionality"`
+6. Modify `login.py`, then commit again
+7. Switch back to main: `git checkout main`
+8. Run `ls` and notice that `login.py` doesn't exist on main!
+9. Switch back to feature-login: `git checkout feature-login`
+10. Run `ls` again and see that `login.py` is back!
+
+> **Important Notes:**
+> - You can use either `git checkout` or `git switch` to change branches
+> - `git checkout -b <name>` creates and switches in one command
+> - `git switch -c <name>` is the newer equivalent
+> - Branches are independent - files in one branch don't affect another until you merge
+> - You can switch between branches as many times as you want
+
+## Key Concepts
+
+- **Branch**: A lightweight movable pointer to a commit. Branches allow you to work on different features independently.
+- **HEAD**: A pointer to the current branch you're working on. When you switch branches, HEAD moves.
+- **main/master**: The default branch name in Git (main is the modern convention, master is older).
+- **Feature Branch**: A branch created to develop a specific feature, separate from the main codebase.
+
+## Useful Commands
+
+```bash
+git branch                   # List all branches (* shows current)
+git branch <name>            # Create a new branch
+git checkout <branch>        # Switch to an existing branch
+git checkout -b <name>       # Create and switch to new branch
+git switch <branch>          # Switch to a branch (newer syntax)
+git switch -c <name>         # Create and switch (newer syntax)
+git branch -d <name>         # Delete a branch (we won't use this yet)
+```
+
+## Verification
+
+Once you've completed the challenge, verify your solution:
+
+```powershell
+.\verify.ps1
+```
+
+The verification script will check that you've created the branch, made commits, and that the branches are independent.
+
+## Need to Start Over?
+
+If you want to reset the challenge and start fresh:
+
+```powershell
+.\reset.ps1
+```
+
+This will remove the challenge directory and run the setup script again, giving you a clean slate.