minor #1345 [StimulusBundle] Added docs on TypeScript support (evertharmeling, weaverryan)

This PR was merged into the 2.x branch.

Discussion
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[StimulusBundle] Added docs on TypeScript support

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Issues        | #1335 <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

Follow-up on #1335, added more info on usage of TypeScript controllers support.

Commits
-------

237164f Tweaking wording
60c0b8e [StimulusBundle] Added docs about Typescript controller usage
3724401 [StimulusBundle] Revert adding var/ to .gitignore

Author: weaverryan

src/StimulusBundle/.gitignore

@@ -1,6 +1,5 @@
 .php-cs-fixer.cache
 .phpunit.result.cache
 composer.lock
-var/
 vendor/
 tests/fixtures/var

src/StimulusBundle/doc/index.rst

@@ -44,7 +44,7 @@ necessary files. If not, or you're curious, see :ref:`Manual Setup <manual-insta
 Usage
 -----
 
-You can now create custom Stimulus controllers inside of the ``assets/controllers.``
+You can now create custom Stimulus controllers inside of the ``assets/controllers``
 directory. In fact, you should have an example controller there already: ``hello_controller.js``:
 
 .. code-block:: javascript
@@ -84,6 +84,14 @@ will activate.
 There's a *lot* more to learn about Stimulus. See the `Stimulus Documentation`_
 for all the goodies.
 
+TypeScript Controllers
+~~~~~~~~~~~~~~~~~~~~~~
+
+If you want to use `TypeScript`_ to define your controllers, you can! Install and set up the
+`sensiolabs/typescript-bundle`_. Then be sure to add the ``assets/controllers`` path to the
+`sensiolabs_typescript.source_dir` configuration. Finally, create your controller in that
+directory and you're good to go.
+
 .. _ux-packages:
 
 The UX Packages
@@ -570,3 +578,5 @@ it will normalize it:
 .. _`Vue`: https://vuejs.org/
 .. _`stimulus-use`: https://stimulus-use.github.io/stimulus-use
 .. _`stimulus-components`: https://stimulus-components.netlify.app/
+.. _`TypeScript`: https://www.typescriptlang.org/
+.. _`sensiolabs/typescript-bundle`: https://github.com/sensiolabs/AssetMapperTypeScriptBundle