UE electrical engineering: add dedicated filter subject with include

docs/vhdl/filter-ueee.md

+{%
+include-markdown  "vhdl/filter.md"
+%}

mkdocs.yml

@@ -82,7 +82,7 @@ nav:
     - FPGA Board Documentation: vhdl/board-docs.md
   - UE Electrical Engineering:
     - Digital synthesizer: vhdl/synthe.md
-    - Audio filter Lab: vhdl/filter.md
+    - Audio filter Lab: vhdl/filter-ueee.md
   - UE MEDCON:
     - Presentation: vhdl/medcon.md
     - Loto Lab: vhdl/loto.md