feat: add more challenges to the history module

01_essentials/02-history/README.md

@@ -7,7 +7,9 @@ In this module, you will:
 - Use `git log` to view commit history with various formats
 - Use `git show` to view specific commit details
 - Use `git diff` to compare changes between commits
+- Use `git diff --staged` to view changes ready to be committed
 - Understand commit hashes and references
+- Discover how `git diff` reveals changes not visible in current files
 
 ## Challenge
 
@@ -23,7 +25,11 @@ This will create a `challenge/` directory with a Git repository that already has
 
 ### Your Task
 
-You'll explore an existing Git repository that contains multiple commits. Your goal is to use Git commands to discover information about the repository's history.
+You'll explore an existing Git repository that contains multiple commits. Your goal is to use Git commands to discover information about the repository's history, including:
+- Viewing commit history
+- Examining changes between specific commits
+- Understanding staged changes
+- **Finding a secret code hidden in the commit history!** (Only discoverable by using `git diff`)
 
 The setup script will create an `answers.md` file in the challenge directory with questions for you to answer. Fill in your answers directly in that file.
 
@@ -31,17 +37,19 @@ The setup script will create an `answers.md` file in the challenge directory wit
 
 1. Navigate to the challenge directory: `cd challenge`
 2. Open `answers.md` to see the questions
-3. View the commit history: `git log`
-4. Try different log formats: `git log --oneline`, `git log --stat`
-5. View specific commits: `git show <commit-hash>`
-6. Compare commits: `git diff <commit1> <commit2>`
-7. Fill in your answers in `answers.md`
+3. View the commit history: `git log` or `git log --oneline`
+4. Check repository status: `git status`
+5. View staged changes: `git diff --staged`
+6. Try different log formats: `git log --stat`, `git log --graph`
+7. View specific commits: `git show <commit-hash>`
+8. Compare specific commits: `git diff <commit1> <commit2> <file>`
+9. Fill in your answers in `answers.md`
 
 > **Important Notes:**
 > - You can use any Git commands you like to explore the repository
 > - Fill in your answers directly in the `answers.md` file (there are placeholder sections for each answer)
-> - Try different `git log` options to see which format you prefer
 > - Commit hashes can be referenced by their full hash or just the first 7 characters
+> - Notice that one file is already staged - use `git diff --staged` to see what it contains
 
 ## Key Concepts
 
@@ -50,6 +58,11 @@ The setup script will create an `answers.md` file in the challenge directory wit
 - **Commit History**: The chronological record of all changes made to a repository.
 - **HEAD**: A pointer to the current commit you're working from.
 - **Diff**: A view showing the differences between two versions of files.
+- **Staging Area**: Where changes wait before being committed. Use `git diff --staged` to see what's ready to commit.
+- **Working Directory vs Staged vs Committed**:
+  - Working Directory: Files you're currently editing
+  - Staged (Index): Changes marked for the next commit (via `git add`)
+  - Committed: Changes permanently saved in history
 
 ## Understanding Diff Output
 
@@ -144,16 +157,23 @@ diff --git a/auth.py b/auth.py
 
 In this module's challenge, you'll use:
 ```bash
-git diff <commit1> <commit2> app.py
+# See what's staged for the next commit
+git diff --staged
+
+# Compare changes between specific commits
+git diff <commit2> <commit4> app.py
 ```
 
 Pay attention to:
 - Which lines were added (green, with `+`)
 - Which lines were removed (red, with `-`)
 - The surrounding context (white, with space)
+- How `git diff --staged` shows only changes ready to commit
 
 ## Useful Commands
 
+### Viewing History
+
 ```bash
 git log                      # View commit history
 git log --oneline            # Compact one-line format
@@ -161,10 +181,29 @@ git log --stat               # Show files changed in each commit
 git log --graph              # Show branch graph (more useful with branches)
 git show <commit>            # View specific commit details
 git show <commit>:<file>     # View a file from a specific commit
-git diff <commit1> <commit2> # Compare two commits
-git diff <commit>            # Compare commit with current working directory
 ```
 
+### Comparing Changes with git diff
+
+```bash
+# Compare commits
+git diff <commit1> <commit2>        # Compare two commits
+git diff <commit1> <commit2> <file> # Compare specific file between commits
+git diff <commit>                   # Compare commit with current working directory
+
+# Compare staged changes
+git diff --staged               # Show changes in staging area (ready to commit)
+git diff --cached               # Same as --staged (alternative syntax)
+git diff                        # Show unstaged changes in working directory
+git diff HEAD                   # Show all changes (staged + unstaged) vs last commit
+```
+
+**When to use each `git diff` variant:**
+- `git diff` - See what you've changed but haven't staged yet
+- `git diff --staged` - Review what you're about to commit
+- `git diff HEAD` - See all your changes since the last commit
+- `git diff <commit1> <commit2>` - Compare any two points in history
+
 ## Verification
 
 Once you've filled in your answers in `answers.md`, verify your solution: