Improve ergonomics when installing from git

Author: dfreeman

README.md

@@ -35,6 +35,7 @@ Use TypeScript in your Ember 2.x and 3.x apps!
   * [Linking Addons](#linking-addons)
   * [In-Repo Addons](#in-repo-addons)
   * [Gotchas](#gotchas)
+* [Installing from git](#installing-from-git])
 * [Current limitations](#current-limitations)
   * [Some `import`s don't resolve](#some-imports-dont-resolve)
   * [Type safety when invoking actions](#type-safety-when-invoking-actions)
@@ -708,6 +709,10 @@ A few things to look out for when working with TypeScript in addons:
 * Normally, addons under development automatically return `true` from their `isDevelopingAddon()` hook, which `ember-cli-typescript` relies on to determine whether to process the addon's `.ts` files. However, if the name field in your `package.json` doesn't match the name in your `index.js`, this default behavior will fail and you'll need to override the method yourself.
 * TypeScript has very particular rules when generating declaration files to avoid letting private types leak out unintentionally. You may find it useful to run `ember ts:precompile` yourself as you're getting a feel for these rules to ensure everything will go smoothly when you publish.
 
+## Installing from git
+
+This addon uses TypeScript for its own implementation, so if you install `ember-cli-typescript` from git rather than from the npm registry, you won't get compiled `.js` files. To get everything working, you can install `ts-node` as a project dependency, and `ember-cli-typescript` will ensure it's registered correctly to transpile source files as needed.
+
 ## Current limitations
 
 While TS already works nicely for many things in Ember, there are a number of corners where it _won't_ help you out. Some of them are just a matter of further work on updating the [existing typings]; others are a matter of further support landing in TypeScript itself, or changes to Ember's object model.

register-ts-node.js

@@ -2,8 +2,17 @@
 
 // eslint-disable-next-line node/no-deprecated-api
 if (!require.extensions['.ts']) {
+  let options = { project: `${__dirname}/ts/tsconfig.json` };
+
+  // If we're operating in the context of another project, which might happen
+  // if someone has installed ember-cli-typescript from git, only perform
+  // transpilation and skip the default ignore glob (which prevents anything
+  // in node_modules from being transpiled)
+  if (process.cwd() !== __dirname) {
+    options.skipIgnore = true;
+    options.transpileOnly = true;
+  }
+
   // eslint-disable-next-line node/no-unpublished-require
-  require('ts-node').register({
-    project: `${__dirname}/ts/tsconfig.json`
-  });
+  require('ts-node').register(options);
 }