debian: Add librem5-flash-image manpage based on help output

debian/clean

+debian/librem5-flash-image.1

debian/control

@@ -5,6 +5,7 @@ Maintainer: Guido Günther <agx@sigxcpu.org>
 Build-Depends:
  debhelper (>= 11),
  flake8,
+ help2man,
  shellcheck,
 Standards-Version: 4.1.3
 Homepage: https://source.puri.sm/Librem5/librem5-devkit-tools/

debian/librem5-host.manpages

+librem5-flash-image.1

debian/rules

 #!/usr/bin/make -f
 
+include /usr/share/dpkg/default.mk
+
 %:
 	dh $@
 
@@ -16,3 +18,9 @@ ifeq (,$(filter nocheck,$(DEB_BUILD_OPTIONS)))
 else
 	@echo "Checks disabled via DEB_BUILD_OPTIONS"
 endif
+
+override_dh_installman:
+	help2man -N --version-string=$(DEB_VERSION_UPSTREAM) \
+		--version-string=0.0.12 scripts/librem5-flash-image \
+		 > debian/tmp/librem5-flash-image.1
+	dh_installman