feat(make): sign more generated binaries (#330)

* doc(make): add not about qemu-user-static

While still investigating https://github.com/ooni/probe/issues/1466

* feat(make): sign more generated binaries

While there, fix an annoying bug where the context manager
was suppressing exceptions that occurred.

Work part of https://github.com/ooni/probe/issues/1466.

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "python.formatting.provider": "black"
+}