1.17 - Add documentation for --pos and --size cmdline args (#591)

* 1.17 - Add documentation for `--pos` and `--size` cmdline args

* Add minor wording tweak

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

TerminalDocs/command-line-arguments.md

@@ -40,6 +40,8 @@ Below is the full list of supported commands and options for the `wt` command li
 | `--fullscreen`, `-F` | Launches the terminal as full screen. |
 | `--focus`, `-f` | Launches the terminal in the focus mode. Can be combined with `maximized`. |
 | `--window`, `-w` `<window-id>` | Launches the terminal in a specific window. |
+| `--pos` `x,y` | (Only available in [Preview](https://aka.ms/terminal-preview)) Launches the terminal at the specified x and y coordinate on the screen. |
+| `--size` `c,r` | (Only available in [Preview](https://aka.ms/terminal-preview)) Launches the terminal with the specified number of columns and rows. |
 
 ### `New-tab` command