Improve the 'soft lockup' issue

- Move to known_issues/graphics because it's about the screen brightness
  and not about first boot stages.
- Name it according to its generic symptom because it affects several
  computer models.

wiki/src/support/known_issues.mdwn

@@ -161,12 +161,6 @@ and it will continue with the boot.
 This problem might be corrected in Tails 1.1 and newer: please report
 your test results back to us.
 
-### Dell XPS 15 9560
-
-To make Tails start successfully, add `acpi_rev_override=1
-nouveau.modeset=0` to the [[startup
-options|/doc/first_steps/startup_options/#boot_loader_menu]].
-
 ### Dell XPS L702X/03RG89, Samsung RV520, Samsung Series 7 Chronos
 
 Does not start on USB sticks created using Tails Installer.

wiki/src/support/known_issues/graphics.mdwn

@@ -294,6 +294,19 @@ We need more test results from users: [[!tails_ticket 15116]]
 Other issues
 ============
 
+Black screen and "soft lockup" error
+------------------------------------
+
+On some laptops, Tails starts but displays the following error and ends
+up on a black screen:
+
+<p class="pre">soft lockup - CPU#<span class="command-placeholder">N</span> stuck for <span class="command-placeholder">N</span>s</p>
+
+To make Tails start successfully, add the following options to the
+[[startup options|/doc/first_steps/startup_options/#boot_loader_menu]]:
+
+    acpi_rev_override=1 nouveau.modeset=0
+
 <a id="sg-black-screen"></a>
 
 Black screen with switchable graphics computers