Updated nomad install documentation and fixed broken links.

docs/explanation/processing.md

docs/howto/customization/basics.md

docs/howto/customization/hdf5.md

docs/howto/oasis/admin.md

docs/howto/oasis/customize.md

docs/howto/oasis/install.md

docs/howto/oasis/plugins_install.md

docs/howto/oasis/update.md

docs/howto/overview.md

docs/howto/plugins/apis.md

docs/howto/plugins/plugins.md

docs/reference/annotations.md

mkdocs.yml