[clang-tidy] Mention std::forward_list in container-size-empty doc (#120701)

Mentioned `std::forward_list` as example of a container without
`size()`.

Author: N-Dekker

clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h

@@ -19,10 +19,10 @@ namespace clang::tidy::readability {
 ///
 /// The emptiness of a container should be checked using the `empty()` method
 /// instead of the `size()`/`length()` method. It shows clearer intent to use
-/// `empty()`. Furthermore some containers may implement the `empty()` method
-/// but not implement the `size()` or `length()` method. Using `empty()`
-/// whenever possible makes it easier to switch to another container in the
-/// future.
+/// `empty()`. Furthermore some containers (for example, a `std::forward_list`)
+/// may implement the `empty()` method but not implement the `size()` or
+/// `length()` method. Using `empty()` whenever possible makes it easier to
+/// switch to another container in the future.
 class ContainerSizeEmptyCheck : public ClangTidyCheck {
 public:
   ContainerSizeEmptyCheck(StringRef Name, ClangTidyContext *Context);

clang-tools-extra/docs/clang-tidy/checks/readability/container-size-empty.rst

@@ -9,9 +9,10 @@ with a call to ``empty()``.
 
 The emptiness of a container should be checked using the ``empty()`` method
 instead of the ``size()``/``length()`` method. It shows clearer intent to use
-``empty()``. Furthermore some containers may implement the ``empty()`` method
-but not implement the ``size()`` or ``length()`` method. Using ``empty()``
-whenever possible makes it easier to switch to another container in the future.
+``empty()``. Furthermore some containers (for example, a ``std::forward_list``)
+may implement the ``empty()`` method but not implement the ``size()`` or
+``length()`` method. Using ``empty()`` whenever possible makes it easier to
+switch to another container in the future.
 
 The check issues warning if a container has ``empty()`` and ``size()`` or
 ``length()`` methods matching following signatures: