Include imported Still Alive data with disclaimer

Commit src/still_alive/imported.h instead of ignoring it. The importer now
writes a source reference (SDSkyKlouD/still-alive-web) and a disclaimer
(Jonathan Coulton / Valve, personal non-commercial use, not affiliated) at
the top of the file; the README carries the same disclaimer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -92,17 +92,26 @@ pio device monitor
 ## Still Alive demo
 
 A recreation of Portal's ending: timed song text typed into a console on the
-left, credits scrolling top right, ASCII art bottom right. Without extra data it
-plays placeholder text. To import the original text, timing, art and credits from
-[SDSkyKlouD/still-alive-web](https://github.com/SDSkyKlouD/still-alive-web):
+left, credits scrolling top right, ASCII art bottom right. The text, timing, art
+and credits in `src/still_alive/imported.h` come from
+[SDSkyKlouD/still-alive-web](https://github.com/SDSkyKlouD/still-alive-web) and can
+be regenerated with:
 
 ```bash
 python tools/import_still_alive.py
 pio run -e still_alive -t upload
 ```
 
-This writes `src/still_alive/imported.h`, which is git-ignored. Reset the board and
-start the song when the serial log says (7.75 s after reset with the imported data).
+Without `imported.h` the demo plays placeholder text. Reset the board and start the
+song when the serial log says (7.75 s after reset with the imported data).
+
+**Disclaimer:** "Still Alive" was written by Jonathan Coulton for Portal (2007).
+Portal, its credits and ASCII art are © Valve Corporation (see
+[Valve Legal Info](https://store.steampowered.com/legal/)); the web recreation they
+are imported from is by [SD SkyKlouD](https://github.com/SDSkyKlouD/still-alive-web).
+They are included only for personal, non-commercial use in this hobby project, and
+all rights remain with their owners. This project is not affiliated with or
+endorsed by Valve.
 
 ## Using the driver