Create demographics-table.md

@ARPeters , can you complete this with your example?

ref #38

snippets/demographics-table.md

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+Different Approaches for Creating Demographics Tables
+=======================
+
+`gtsummary::tbl_summary()`
+--------------------------------
+
+* Purpose: Create a table with three variables (gender, race, & ethnicity) for manuscript
+* Logic: Leverage the capabilities build into [`gtsummary::tbl_summary()`](https://www.danieldsjoberg.com/gtsummary/articles/tbl_summary.html)
+* Last reviewed date: 2023-10-16 by Andrew Peters
+* Example projects:
+  * [bergner-human-milk-3, analysis-3.Rmd](https://github.com/OuhscBbmc/bergner-human-milk-3/tree/main/analysis/analysis-3)
+
+Code:
+
+```r
+bla bla
+```