Update the purpose of reset --hard and explain how to undo it with the ref log

Author: Michael Friedrich

day1/03_Basics/03_Changes.md

@@ -25,7 +25,7 @@ manually move the file, you will need to rm and add it again.
 * `git reset`
   * Reset files added to the staging index.
   * Reset and drop commits
-  * `--soft` keeps the changes (default), `--hard` removes them indefinitely.
+  * `--soft` keeps the changes (default), `--hard` removes them.
 * `git rm`
   * Remove the file(s) from working tree and Git repository.
   * Note that file(s) will be visible in Git history, and can be restored from it.
@@ -34,7 +34,12 @@ manually move the file, you will need to rm and add it again.
 
 ****
 
-`git reset` resets files added to the staging index.
+`git reset` resets files added to the staging index. You can also use it to
+reset commits from the history.
+
+Hint: If you are using a `--hard` reset, you can still undo the change
+with the help of the ref log where git stores "meta" information about
+any change: `git reset --hard HEAD@{1}`.
 
 `git rm` removes the file from the working tree and also from the git index.
 

day2/01_Workflows/02_Centralized.md

@@ -199,7 +199,7 @@ The last parameter specifies the target directory `training2`.
 * Objective:
  * Rebase your local history with the remote repository
 * Steps:
- * Reset the local history by 2 commits with `git reset --hard HEAD~2`
+ * Simulate two commits in the past: `git reset --hard HEAD~2`
  * Update and commit README.md
  * Fetch remote and compare with `git diff origin/master`
  * Rebase with `git rebase origin/master`
@@ -237,7 +237,7 @@ instead of generating a merge commit.
 ****
 
 * Change into `$HOME/training`
-* Reset the local history by 2 commits with `git reset --hard HEAD~2`
+* Simulate two commits in the past: `git reset --hard HEAD~2`
 * Update and commit README.md
 * Fetch the remote repository and use `git diff origin/master` to compare the changes
 * Rebase the master branch against the remote master branch with `git rebase origin/master`
@@ -252,7 +252,10 @@ instead of generating a merge commit.
 
 ****
 
-### Reset the history by 2 commits
+### Simulate two commits in the past
+
+This is just for testing the rebase laster on with different commit history
+branches. Commits can be reset from the history with the following command:
 
     @@@ Sh
     $ git reset --hard HEAD~2