Fix broken links inside app

Summary:
Searched for broken link patterns inside the app itself. I think I found them all but it's not certain.

Patterns searched for and replaced:
```
.html
getting-started/)
getting-started)
getting-started"
```

and also searched the repo for regex `\]\(.*)` and checked them by eye.

Reviewed By: passy

Differential Revision: D21306944

fbshipit-source-id: a2e09b0fd8677f5f26e5cc4a06805b474247f7e6

desktop/pkg/src/commands/lint.ts

@@ -35,7 +35,7 @@ export default class Lint extends Command {
       const errors = await runLint(inputDirectory);
       if (errors) {
         this.error(
-          `Plugin package definition is invalid. See https://fbflipper.com/docs/extending/js-setup.html#plugin-definition for details.\n${errors.join(
+          `Plugin package definition is invalid. See https://fbflipper.com/docs/extending/js-setup#plugin-definition for details.\n${errors.join(
             '\n',
           )}`,
         );