update day 1 slides

Author: ahasverus

_site.yml

@@ -25,13 +25,13 @@ navbar:
       - text: "The Protocol"
         href: "courses/the-protocol.pdf"
       - text: "Formulating questions"
-        href: "#"
+        href: "courses/knowledge_synthesis.pdf"
       - text: "Literature search"
-        href: "courses/literature-search.pdf"
+        href: "courses/knowledge_synthesis.pdf"
       - text: "Corpus management"
         href: "https://literaturesynthesis.github.io/corpus-management"
       - text: "Article screening"
-        href: "courses/selection-eligibility.pdf"
+        href: "courses/knowledge_synthesis.pdf"
       - text: "Retrieving full texts"
         href: "https://literaturesynthesis.github.io/retrieving-fulltext"
       - text: "DAY 2"