Document trimBlockSelection setting (#313)

* Document trimBlockSelection setting

* Add preview disclaimer

* Minor edit + note re how to select rectangular txt

* Add preview to h2

Co-authored-by: Matt Wojciakowski <mattwoj@microsoft.com>

TerminalDocs/customize-settings/interaction.md

@@ -44,6 +44,25 @@ When this is set to `true`, the color and font formatting of the selected text i
 
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+## Remove trailing white-spaces when copying text in rectangular selection to clipboard (preview)
+
+When this is set to `true` and you copy text in a rectangular (block) selection to the clipboard, trailing white-spaces are removed from each line. When it's set to `false`, the white-spaces are preserved, ensuring that all lines have the same length. To copy text in a rectangular (block) selection, hold down the `Alt` key, right-click and drag your mouse over the text area you want to select. This can be useful for selecting text columns, etc.
+
+**Property name:** `trimBlockSelection`
+
+**Necessity:** Optional
+
+**Accepts:** `true`, `false`
+
+**Default value:** `false`
+
+> [!IMPORTANT]
+> This feature is only available in [Windows Terminal Preview](https://aka.ms/terminal-preview).
+
+<br />
+
+___
+
 ## Word delimiters
 
 This determines the word delimiters used in a double-click selection. Word delimiters are characters that specify where the boundary is between two words. The most common examples are spaces, semicolons, commas, and periods.