Issue #730: Add Sentinel Core ITX motherboard.

Author: geerlingguy

_boards_cm/sentinel-core.md

@@ -0,0 +1,10 @@
+---
+layout: board
+title: "Sentinel Core"
+short_description: Mini ITX motherboard for CM5 with full-size PCIe slot.
+status: prototype
+picture: "/images/board-sentinel-core.jpg"
+github_issue: "https://github.com/geerlingguy/raspberry-pi-pcie-devices/issues/730"
+link: https://sanctuary-systems.com/sentinel-core/
+videos: []
+---