deallocvt: add page (#23678)

Co-authored-by: Wiktor Perskawiec <wiktor@perskawiec.cc>

Author: Malik740

pages/common/deallocvt.md

@@ -0,0 +1,20 @@
+# deallocvt
+
+> Deallocate unused virtual consoles.
+> More information: <https://manned.org/deallocvt>.
+
+- Free all unused consoles:
+
+`deallocvt`
+
+- Deallocate a specific console:
+
+`deallocvt {{[-C|--console]}} {{/dev/ttyN}}`
+
+- Display help:
+
+`deallocvt {{[-h|--help]}}`
+
+- Display version:
+
+`deallocvt {{[-V|--version]}}`