Adding more of the exercises for the commits section

Author: bbrydsoe

docs/commits-exercises.md

@@ -55,3 +55,28 @@ Enter the `repository/` directory under `git_materials/4.commits/2.recover_head`
     - rev-parse
     - cat .git/something
 
+## 3. Stashing uncommitted changes
+
+!!! note 
+
+    The goal of this exercise is to learn to checkout a different commit and stash uncommited changes, if necessary. 
+
+Enter the `repository/` directory under `git_materials/4.commits/3.stash` and perform the following steps: 
+
+1. Identify the first commit (`This is going to be a cake recipe`).
+2. Try to checkout the commit in order to identify the initial title of the recipe. If necessary, stash the changes. What was the initial title of the recipe?
+3. Restore the `HEAD` and pop the changes from the stash.
+4. Confirm that the changes were applied correctly and that the stash is empty.
+
+## 4. Discarding the latest commit 
+
+!!! note 
+
+    The goal of this exercise is to learn to discard the latest commit. 
+
+Enter the `repository/` directory under `git_materials/4.commits/4.discard` and perform the following steps: 
+
+1. Discard the latest commit. Also discard the changes in the working tree.
+2. Confirm that the commit is no longer reachable from `master`. Confirm that the `recipe.txt` no longer contains the section "Other ideas and hints".
+3. Try to restore the discarded commit. (optional)
+