Adds a section to README

Adds a Doing More section with a couple of references where I know that I've shared custom functions here. I'm not sure this is the best place to put this. 

I think that many issues might be helped by people having more familiarity with custom functions and there use.  Is there a "it worked for me" or gallery section where users can post successful function examples with their output and the problem they were solving? I see this on SO, but maybe users are going here first?

README.Rmd

@@ -129,6 +129,18 @@ formattable(df, list(
 
 `formattable` will automatically convert to an `htmlwidget` when in an `interactive()` context such as the console or RStudio IDE.  If you would like to avoid this conversion and see the `html` table output, please use `format_table()` that calls `knitr::kable()` with formatters or call `format()` with the `formattable data.frame` object.
 
+## Doing More
+
+Much of the power of formattable can be harnessed by writing custom functions that make your formatting the way you need it. 
+
+For example, 
+do you need to pass a formatting function with no arguments to use the `area`? Write a custom function with one argument
+ - see [issue 99 comment](https://github.com/renkun-ken/formattable/issues/99#issuecomment-943841474)
+do you need to make a custom tile that uses more than two colours and is colour aware? Write a custom function 
+ - see [issue 113 comments](https://github.com/renkun-ken/formattable/issues/113#issuecomment-575678017)
+
+
+
 ## License
 
 This package is under [MIT License](https://opensource.org/licenses/MIT).