Added this changelog

Added Section 6.6, “Creating containers from current HPC environment” (Jira)

Added notes about dolly, memkind, openblas, spack, and mpich in Section 6, “Changes affecting all architectures”

Added note about Ganglia being unsupported in Section 7, “Removed and deprecated features and packages” (Jira)

Added note about removal of Python 2 bindings for genders (Jira)

Added a note about building libraries using spack in Section 7, “Removed and deprecated features and packages” (Jira)

Added adios and superlu to the list of removed libraries in Section 7, “Removed and deprecated features and packages”