Install dependencies on RHEL and CentOS

For RHEL and CentOS, GMT's dependencies are available from Extra Packages for Enterprise Linux. You can add this repository by telling yum:

# Enable the EPEL repository
sudo yum install epel-release
# For RHEL/CentOS 8, you also need to enable the powertools repository
sudo yum config-manager --set-enabled powertools

You then can install the GMT dependencies with:

# Install necessary dependencies
sudo yum install cmake libcurl-devel netcdf-devel gdal-devel

# Install optional dependencies
sudo yum install ninja-build gdal pcre-devel fftw3-devel lapack-devel openblas-devel glib2-devel ghostscript

# to enable movie-making
# ffmpeg is provided by [rmpfusion](https://rpmfusion.org/)
sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/free/el/rpmfusion-free-release-`rpm -E %rhel`.noarch.rpm
sudo yum install GraphicsMagick ffmpeg

# to enable document viewing via gmt docs
sudo yum install xdg-utils

# to enable testing
sudo yum install GraphicsMagick

# to build the documentation
sudo yum install python3-sphinx