Clarify README for tsx/jsx endings. (#1179)

* Clarify README for tsx/jsx endings.

* Make wording less ambiguous

* Update README.md

* Update README.md

Co-authored-by: Andrew Bradley <cspotcode@gmail.com>

README.md

@@ -139,7 +139,10 @@ Create a new Node.js configuration and add `-r ts-node/register` to "Node parame
 
 ## How It Works
 
-**TypeScript Node** works by registering the TypeScript compiler for `.tsx?` and `.jsx?` (when `allowJs == true`) extensions. When node.js has an extension registered (via `require.extensions`), it will use the extension internally for module resolution. When an extension is unknown to node.js, it handles the file as `.js` (JavaScript). By default, **TypeScript Node** avoids compiling files in `/node_modules/` for three reasons:
+**TypeScript Node** works by registering the TypeScript compiler for `.ts`, `.tsx`, `.js`, and `.jsx` extensions.
+`.js` and `.jsx` are only registered when [`allowJs`](https://www.typescriptlang.org/docs/handbook/compiler-options.html#compiler-options) is enabled.
+`.tsx` and `.jsx` are only registered when [`jsx`](https://www.typescriptlang.org/docs/handbook/jsx.html) is enabled.
+When node.js has an extension registered (via `require.extensions`), it will use the extension internally for module resolution. When an extension is unknown to node.js, it handles the file as `.js` (JavaScript). By default, **TypeScript Node** avoids compiling files in `/node_modules/` for three reasons:
 
 1. Modules should always be published in a format node.js can consume
 2. Transpiling the entire dependency tree will make your project slower