add LF copyright statement to spack.io

_config.yml

@@ -26,6 +26,7 @@ baseurl                  : # the subpath of your site, e.g. "/blog"
 repository               : # GitHub username/repo-name e.g. "mmistakes/minimal-mistakes"
 teaser                   : ""
 logo                     : /assets/images/spack-logo.svg
+copyright                : Spack Project</a>, a Series of LF Projects, LLC. For web site terms of use, trademark policy and other project policies please see <a href="https://lfprojects.org">lfprojects.org</a>
 masthead_title           : # overrides the website title displayed in the masthead, use " " for no title
 # breadcrumbs            : false # true, false (default)
 words_per_minute         : 200