Available on Hulu by way of FX, “Say Nothing” is a luminous adaptation of the book of the same name written by Patrick Radden Keefe. Its subject is the Troubles in Northern Ireland, the decades of strife centered at Belfast that consumed the Emerald Isle between the 1960s and the Good Friday Agreement of 1998. Call it a war, a rebellion, an insurgency, or what you will — it was a brutal snarl of intimate violence over how the North was to be ruled.