#47 add release notes

doc/release-notes/47-solr-upgrade.md

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+### Solr 8 Support/Upgrade
+
+The Dataverse Software now runs on Solr 8.11.1, the latest available stable release in the Solr 8.x series.
+
+### Solr Upgrade
+
+With this release we upgrade to the latest available stable release in the Solr 8.x branch. We recommend a fresh installation of Solr 8.8.1 (the index will be empty) followed by an "index all".
+
+Before you start the "index all", the Dataverse installation will appear to be empty because the search results come from Solr. As indexing progresses, partial results will appear until indexing is complete.
+
+See <http://guides.dataverse.org/en/5.10/installation/prerequisites.html#installing-solr> for more information.