Make "Automatic installer" command a copy-able code block (#2874)

README.md

@@ -238,7 +238,9 @@ As far as Pyenv is concerned, version names are simply directories under
 
 ##### Automatic installer
 
-`curl https://pyenv.run | bash`
+```bash
+curl https://pyenv.run | bash
+```
 
 For more details visit our other project:
 https://github.com/pyenv/pyenv-installer