Add troubleshooting for title attributes during layout restoring. (#2679)

docs/layout-saving

@@ -259,3 +259,27 @@ container:
     ]
 }
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+
+=== Placeholders using window title matches don't swallow the window
+
+If you use the +title+ attribute to match a window and find that it doesn't
+work or only works sometimes, the reason might be that the application sets the
+title only after making the window visible. This will be especially true for
+programs running inside terminal emulators, e.g., +urxvt -e irssi+ when
+matching on +title: "irssi"+.
+
+One way to deal with this is to not rely on the title, but instead use, e.g.,
+the +instance+ attribute and running the program to set this window instance to
+that value:
+
+--------------------------------------------------------------------------------
+# Run irssi via
+# urxvt -name "irssi-container" -e irssi
+
+"swallows": [
+    {
+        "class": "URxvt",
+        "instance": "irssi-container"
+    }
+]
+--------------------------------------------------------------------------------