doc: add link to unofficial playground

PR #2760

README.md

@@ -220,6 +220,16 @@ configuration files, passthru, support for searching compressed files,
 multiline search and opt-in fancy regex support via PCRE2.
 
 
+### Playground
+
+If you'd like to try ripgrep before installing, there's an unofficial
+[playground](https://codapi.org/ripgrep/) and an [interactive
+tutorial](https://codapi.org/try/ripgrep/).
+
+If you have any questions about these, please open an issue in the [tutorial
+repo](https://github.com/nalgeon/tryxinyminutes).
+
+
 ### Installation
 
 The binary name for ripgrep is `rg`.