Add libguides and researchdatabases sources

Why these changes are being introduced:
* With two new sources added to transmogrifier, they will need to be added in this project as well to allow for indexing to OpenSearch.

How this addresses that need:
* Adding the source names to VALID_SOURCES allows them to be indexed.

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/TIMX-227

Author: ghukill

.gitignore

@@ -155,3 +155,4 @@ cython_debug/
 .DS_Store
 output/
 .vscode/
+.idea/