add a reference to Tidyverse, IE notation, and Barker's notation

Author: dimitri-yatsenko

book/30-schema-design/055-normalization.ipynb

@@ -207,7 +207,7 @@
       "cell_type": "markdown",
       "metadata": {},
       "source": [
-        "\n"
+        "The principles of normalization have been more recently rediscovered and recast in more accessible terms for tables used in the R programming language under the names \"tidy data\" [doi.org/10.18637/jss.v059.i10] and \"tidyverse\" [@10.1093/bioinformatics/btx355]."
       ]
     },
     {