gnuchess: add page (#22173)

Co-authored-by: Ivan Baluta <ivanbaluta.dev@gmail.com>

pages/common/gnuchess.md

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+# gnuchess
+
+> Play chess against an engine.
+> More information: <https://www.gnu.org/software/chess/manual/gnuchess.html#Running-GNU-Chess>.
+
+- Start an interactive chess game:
+
+`gnuchess`
+
+- [Interactive] Play a move using algebraic notation:
+
+`{{e4}}`
+
+- Enable graphic mode, showing chess pieces instead of letters:
+
+`gnuchess {{[-g|--graphic]}}`
+
+- Display engine output:
+
+`gnuchess {{[-p|--post]}}`
+
+- [Interactive] Exit `gnuchess`:
+
+`quit`