Add an explicit first step in wireless section

Mention that the device must be plugged via USB before configuring
TCP/IP connections.

It wasn't obvious that the device should be first plugged before running
scrcpy wirelessly, especially to those who aren't very familiar with
adb.

Note from committer: add this new step with index 0 to make the diff
readable, the next commit will renumber all the steps.

PR #1303 <https://github.com/Genymobile/scrcpy/pull/1303>

Signed-off-by: Romain Vimont <rom@rom1v.com>

README.md

@@ -404,6 +404,7 @@ connect to the device before starting.
 Alternatively, it is possible to enable the TCP/IP connection manually using
 `adb`:
 
+0. Plug the device into a USB port on your computer.
 1. Connect the device to the same Wi-Fi as your computer.
 2. Get your device IP address, in Settings → About phone → Status, or by
    executing this command: