Update enclosure design & add assembly instructions

- The holes for HD-BNC headers GND pins are enlarged
- Remove the U-shape cutout for the HD-BNC headers in Case_Bottom Part
- Add assembly instructions to README

Enclosure/README.md

@@ -24,4 +24,10 @@ For nix-os user, running `nix develop` and then `freecad` can start the FreeCad.
 
 # Production
 
-Case_Top and Case_Bottom parts are needed to be 3D printed in high resolution 3D printer (Tolerance: ± 0.1 mm) in ESD Safe material (like ESD-ABS7). All three parts (PCB, Case Top, Case Bottom) are secured with two M2 x 7 Screw. Two M2 heat set threads are needed to be installed to the Case Bottom part before assembly.
+Case_Top and Case_Bottom parts are needed to be 3D printed in high resolution 3D printer (Tolerance: ± 0.1 mm) in ESD Safe material (like ESD-ABS7). All three parts (PCB, Case_Top, Case_Bottom) are secured with two M2 x 7 PEEK Plastic screws. If you cannot source M2 x 7 PEEK Plastic screws, you should source M2 x 8 PEEK Plastic screws and cut the protruding part after installation. Two M2 x 3 heat set threaded inserts are needed to be installed to the Case_Bottom part before assembly.
+
+## Assembly Instructions
+
+1. Install the threaded inserts to top side of the Case_Bottom part. The illustration image shown above is the top side. The installed threaded inserts should be aligned to the surface of the Case_Bottom part.
+2. Place the PCB into the Case_Bottom Part. The PCB surface should not protrude above the edge rail.
+3. Slide the Case_Top part into the Case_Bottom part and then fasten the screws. Cut the protruding screws if M2 x 8 or longer screws are used.