Remove statement that data is moved when assigning (#982)

* Remove statement that data is moved when assigning

The distinction between non-`Copy` and `Copy` types is tricky to explain. One problem is that people often focus on _moving_ vs _copying_ when both variable types always copy data.

This PR removes the statement about moving data (since that is wrong on its own).

* Apply suggestions from code review

Co-authored-by: Dustin J. Mitchell <djmitche@google.com>

* Apply suggestions from code review

Co-authored-by: Dustin J. Mitchell <djmitche@google.com>

---------

Co-authored-by: Dustin J. Mitchell <djmitche@google.com>

src/ownership/move-semantics.md

@@ -1,6 +1,6 @@
 # Move Semantics
 
-An assignment will transfer ownership between variables:
+An assignment will transfer _ownership_ between variables:
 
 ```rust,editable
 fn main() {
@@ -12,8 +12,7 @@ fn main() {
 ```
 
 * The assignment of `s1` to `s2` transfers ownership.
-* The data was _moved_ from `s1` and `s1` is no longer accessible.
-* When `s1` goes out of scope, nothing happens: it has no ownership.
+* When `s1` goes out of scope, nothing happens: it does not own anything.
 * When `s2` goes out of scope, the string data is freed.
 * There is always _exactly_ one variable binding which owns a value.
 
@@ -21,6 +20,10 @@ fn main() {
 
 * Mention that this is the opposite of the defaults in C++, which copies by value unless you use `std::move` (and the move constructor is defined!).
 
+* It is only the ownership that moves. Whether any machine code is generated to manipulate the data itself is a matter of optimization, and such copies are aggressively optimized away.
+
+* Simple values (such as integers) can be marked `Copy` (see later slides).
+
 * In Rust, clones are explicit (by using `clone`).
 
 </details>