message: Update README.md
  Adding a note about a gotcha that I spent some time working out. Feel free to put the note somewhere else if what I did isn't the right organization.
diff: Installation
  ---
  -From NPM:
  +From npm:
  npm install recast
  @@ -158,6 +158,8 @@ const tsAst = recast.parse(source, {
  **Note:** Some of these parsers import npm packages that Recast does not directly depend upon, so please be aware you may have to run `npm install babylon@next` to use the `typescript`, `flow`, or `babylon` parsers, or `npm install acorn` to use the `acorn` parser. Only Esprima is installed by default when Recast is installed.
  +After calling `recast.parse`, if you're going to transform the AST, make sure that the `.original` property is preserved. With Babel, for instance, if you call `transformFromAST`, you must pass `cloneInputAst: false` in its options. ([More detail](https://github.com/babel/babel/issues/12882).
  +
  Source maps
  ---
  