fix small ambiguity in tutorial

[zooko]

I momentarily misparsed this, thinking that lending X a reference to Y would freeze X. This patch fixes it for me:

diff --git a/src/doc/tutorial.md b/src/doc/tutorial.md
index b712294..5727141 100644
--- a/src/doc/tutorial.md
+++ b/src/doc/tutorial.md
@@ -1473,7 +1473,7 @@ For a more in-depth explanation of references and lifetimes, read the

 ## Freezing

-Lending an &-pointer to an object freezes it and prevents mutation—even if the object was declared as `mut`.
+Lending an &-pointer to an object freezes the pointed-to object and prevents mutation—even if the object was declared as `mut`.
 `Freeze` objects have freezing enforced statically at compile-time. An example
 of a non-`Freeze` type is [`RefCell<T>`][refcell].

[steveklabnik]

Thank you! Would you mind submitting it as a pull request?

[steveklabnik]

Nevermind, I just did it myself :) Thanks for pointing it out!

[zooko]

So can we close this issue ticket now?