doc: build the top-level README as a single rule
doc: build the top-level README as a single rule

2 rules with intermediate file being removed means
that those rules always rerun.

shekkbuilder/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc,shekkbuilder/hwloc,ggouaillardet/hwloc,shekkbuilder/hwloc