README for the data.

README.md

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+# Data files for intro workshop
+
+- `gapminder.csv`: Entire GapMinder dataset
+    - `gapminder-5060.csv`: 1950s and 1960s
+    - `gapminder-7080.csv`: 1970s and 1980s
+    - `gapminder-90plus.csv`: 1990s onwards
+
+- **Important note about `gapminder-5060.csv`:
+    - The dataset has been altered to add a "data error".
+    - Life expectancy for Canada in the year 1967 is coded
+    as `999999`, it should actually be `69.96`.
+    - For details see [intro-01-slides.Rmd](https://github.com/Reproducible-Science-Curriculum/rr-intro/blob/master/intro-01-slides.Rmd).
+    - `gapminder-5060_original.csv` contains the correct data.