Add information about refactoring support

[rainbyte]

Probably a refactoring-specific chart would be needed, because there are various items to compare.

At least the following ones should be mentioned:

• Rename symbol
• Extract function
• Delete unused code (e.g. unused non-exported function)
• Change scope (e.g. move to let or where)
• Add/remove function argument
• Inline definition (replace a function with its body)
• Expand TH macro (I think this was mentioned on reddit)