Merge pull request #1118 from erinmgraham/fix-head-issue-1080

simplify explanations of git diff head

Author: erinmgraham

episodes/04-changes.md

@@ -286,8 +286,6 @@ but we haven't told Git we will want to save those changes
 nor have we saved them (which we do with `git commit`).
 So let's do that now. It is good practice to always review
 our changes before saving them. We do this using `git diff`.
-This shows us the differences between the current state
-of the file and the most recently saved version:
 
 ```bash
 $ git diff
@@ -447,12 +445,9 @@ $ git add guacamole.md
 $ git diff
 ```
 
-There is no output:
-as far as Git can tell,
-there's no difference between what it's been asked to save permanently
-and what's currently in the directory.
-However,
-if we do this:
+There is no output. Without any arguments, `git diff` compares the working directory and the staging area. After `git add`, the two versions are identical and there is nothing to show.
+
+However, if we do this:
 
 ```bash
 $ git diff --staged
@@ -473,10 +468,7 @@ index 315bf3a..b36abfd 100644
  ## Instructions
 ```
 
-it shows us the difference between
-the last committed change
-and what's in the staging area.
-Let's save our changes:
+we can see that by adding the `--staged` argument to the command we are now comparing what’s in the staged area to the last committed change.
 
 ```bash
 $ git commit -m "Modify guacamole to the traditional recipe"

episodes/05-history.md

@@ -22,12 +22,12 @@ exercises: 0
 ::::::::::::::::::::::::::::::::::::::::::::::::::
 
 As we saw in the previous episode, we can refer to commits by their
-identifiers.  You can refer to the *most recent commit* of the working
-directory by using the identifier `HEAD`.
+identifiers. Git also provides a special identifier called `HEAD`, which refers to the **most recent commit**.
 
-We've been adding small changes at a time to `guacamole.md`, so it's easy to track our
-progress by looking, so let's do that using our `HEAD`s.  Before we start,
-let's make a change to `guacamole.md`, adding yet another line.
+We can use `HEAD` together with commands we already know to examine our project’s history.
+
+Before we start, let's make a change to `guacamole.md` so we have something
+to compare. We won’t save this change yet.
 
 ```bash
 $ nano guacamole.md
@@ -62,7 +62,9 @@ index b36abfd..0848c8d 100644
 +An ill-considered change
 ```
 
-Note that `HEAD` is the default option for `git diff`, so omitting it will not change the command's output at all (give it a try). However, the real power of `git diff` lies in its ability to compare with previous commits. For example, by adding `~1` (where "~" is "tilde", pronounced [**til**\-d*uh*]), we can look at the commit before `HEAD`.
+Here we have the difference between the file in our working directory and the most recently committed version. 
+
+We can also refer to earlier commits relative to `HEAD`. For example, by adding `~1` (where "~" is "tilde", pronounced [**til**\-d*uh*]), we can look at the commit before `HEAD`.
 
 ```bash
 $ git diff HEAD~1 guacamole.md