Say how the transmit pane works and what would make it exact

The pump is paced off the clock. XMMT.ocx has a TxBufLen property and answers
when it is asked, so the bridge could report what the engine still holds and
make the red text exact, but the engine does not start on this machine and the
property could not be watched while a message was going out.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

README.md

@@ -47,6 +47,7 @@ scorer: red for a dupe, green for a new multiplier, blue for points.
 | Contests | CQ WW (CW, SSB, RTTY), CQ WPX (CW, SSB, RTTY), WAE (CW, SSB, RTTY), ARRL DX, IARU HF, Sweepstakes, RTTY Roundup, NAQP, OK/OM DX (CW), YOTA, IOTA, EU DX Contest, CQ 160, ARRL 10M, REF, Ukrainian DX, Russian DX RTTY, RDAC, YO DX HF, Oceania DX, All Asian, SARTG RTTY, BARTG Sprint, Mexico RTTY, IARU Region 1 Field Day, general logging, and user-defined `.udc` contests |
 | Log | N1MM `.s3db`, Cabrillo 3.0 out, ADIF in and out |
 | While typing | dupe check, multiplier check, points, country and zone from the country file, exchange filled from a call history file |
+| While transmitting | a digital message is held in the transmit pane and fed to the engine a character at a time, so what has not gone out can still be rewritten; what has gone out is red, and the engine idles when it catches up with the cursor |
 | Windows | entry, log, check, bandmap, available mults and Qs, score summary, grey line, telnet, digital interface |
 | Editing | double-click a cell in the log, or open the whole contact with Ctrl+Y; Delete removes it. All of it goes out to the other stations |
 | Radio | one or two radios over hamlib `rigctld`, split, reconnecting on its own |