add GitHub repo with slides

.gitmodules

+[submodule "adv_scrnaseq_2020"]
+	path = adv_scrnaseq_2020
+	url = https://github.com/fmicompbio/adv_scrnaseq_2020.git

adv_scrnaseq_2020 @ 1e4926fc

+Subproject commit 1e4926fc686a58af971844858abd1e85784a38a2

adv_scrnaseq_2020.Rproj

+Version: 1.0
+
+RestoreWorkspace: Default
+SaveWorkspace: Default
+AlwaysSaveHistory: Default
+
+EnableCodeIndexing: Yes
+UseSpacesForTab: Yes
+NumSpacesForTab: 2
+Encoding: UTF-8
+
+RnwWeave: Sweave
+LaTeX: pdfLaTeX