Makefile recommends yum, when dnf is more current

[trafalmuffti]

open-source-search-engine/Makefile

Lines 183 to 190 in 9146f05

	@echo "If make fails on RedHat then first run:"
	@echo ""
	@echo "sudo yum install gcc-c++"
	@echo ""
	@echo ""
	@echo "If make fails on CentOS then first run:"
	@echo ""
	@echo "sudo yum install gcc-c++ openssl-devel"

Makefile recommends yum, when dnf is more current on modern RedHat derived distributions.

[onlyjob]

IMHO those comments are better to be moved to README.

Also, isn't yum is just a symbolic link to dnf? If so then they are identical, although using dnf in docs is probably more correct.

[onlyjob]

I have moved build instructions to README in 857a62d but docs still need to be modernised for current distros.