Improved README formatting. (#25808)

Author: gromag

doc/cheatsheet/README.txt

@@ -1,8 +1,8 @@
 The Pandas Cheat Sheet was created using Microsoft Powerpoint 2013.
 To create the PDF version, within Powerpoint, simply do a "Save As"
-and pick "PDF' as the format.
+and pick "PDF" as the format.
 
-This cheat sheet was inspired by the RstudioData Wrangling Cheatsheet[1], written by Irv Lustig, Princeton Consultants[2].
+This cheat sheet was inspired by the RStudio Data Wrangling Cheatsheet[1], written by Irv Lustig, Princeton Consultants[2].
 
 [1]: https://www.rstudio.com/wp-content/uploads/2015/02/data-wrangling-cheatsheet.pdf
 [2]: http://www.princetonoptimization.com/