How-to-guide.md

@@ -14,3 +14,5 @@ The folder `ete3` is located within the `.../lib/pythonX.X/site-package` folder
 
 
 Reference : https://github.com/etetoolkit/ete/issues/173
+
+If it remains unclear : https://gitlab.mbb.univ-montp2.fr/edna/custom_reference_database/-/issues/4
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