Revert back accidentally removed {layout} placeholder

...and also rewrite the first sentence in the related paragraph in
README and NEWS - there are more placeholders that support formatting
than those that do not.  It would have been clear from the diff if
these files weren't wrapped...

I accidentally removed it in commit
cae756bab8.

NEWS.md

@@ -1,10 +1,10 @@
 swayr v0.13.0
 =============
 
-- The placeholders `{id}`, `{app_name}`, `{name}`/`{title}`, `{output_name}`,
+- All the placeholders except `{app_icon}`, `{indent}`, `{urgency_start}`, and
-  `{workspace_name}`, and `{marks}` may optionally provide a format string as
+  `{urgency_end}` may optionally provide a format string as specified by
-  specified by [Rust's std::fmt](https://doc.rust-lang.org/std/fmt/).  The
+  [Rust's std::fmt](https://doc.rust-lang.org/std/fmt/).  The syntax is
-  syntax is `{<placeholder>:<fmt_str><clipped_str>}`.  For example,
+  `{<placeholder>:<fmt_str><clipped_str>}`.  For example,
   `{app_name:{:>10.10}}` would mean that the application name is printed with
   exactly 10 characters.  If it's shorter, it will be right-aligned (the `>`)
   and padded with spaces, if it's longer, it'll be cut after the 10th

README.md

@@ -324,17 +324,17 @@ right now.
 * `fallback_icon` is a path to some PNG/SVG icon which will be used as
   `{app_icon}` if no application-specific icon can be determined.
 
-The placeholders `{id}`, `{app_name}`, `{name}`/`{title}`, `{output_name}`,
+All the placeholders except `{app_icon}`, `{indent}`, `{urgency_start}`, and
-`{workspace_name}`, and `{marks}` may optionally provide a format string as
+`{urgency_end}` may optionally provide a format string as specified by
-specified by [Rust's std::fmt](https://doc.rust-lang.org/std/fmt/).  The syntax
+[Rust's std::fmt](https://doc.rust-lang.org/std/fmt/).  The syntax is
-is `{<placeholder>:<fmt_str><clipped_str>}`.  For example,
+`{<placeholder>:<fmt_str><clipped_str>}`.  For example, `{app_name:{:>10.10}}`
-`{app_name:{:>10.10}}` would mean that the application name is printed with
+would mean that the application name is printed with exactly 10 characters.  If
-exactly 10 characters.  If it's shorter, it will be right-aligned (the `>`) and
+it's shorter, it will be right-aligned (the `>`) and padded with spaces, if
-padded with spaces, if it's longer, it'll be cut after the 10th character.
+it's longer, it'll be cut after the 10th character.  Another example,
-Another example, `{app_name:{:.10}...}` would mean that the application name is
+`{app_name:{:.10}...}` would mean that the application name is truncated at 10
-truncated at 10 characters.  If it's shorter, it will be printed as-is (no
+characters.  If it's shorter, it will be printed as-is (no padding), if it's
-padding), if it's longer, it'll be cut after the 10th character and the last
+longer, it'll be cut after the 10th character and the last 3 characters of that
-3 characters of that substring will be replaced with `...` (`<clipped_str>`).
+substring will be replaced with `...` (`<clipped_str>`).
 
 It is crucial that during selection (using wofi or some other menu program)
 each window has a different display string.  Therefore, it is highly

src/tree.rs

@@ -516,6 +516,7 @@ impl DisplayFormat for DisplayNode<'_> {
                 let value = match &caps["name"] {
                     "id" => self.node.id.to_string(),
                     "app_name" => self.node.get_app_name().to_string(),
+                    "layout" => format!("{:?}", self.node.layout),
                     "name" | "title" => self.node.get_name().to_string(),
                     "output_name" => self
                         .tree