Expose docs for the Rails FormControl component

Author: camertron

content/components/form-control.mdx

@@ -2,6 +2,8 @@
 title: Form control
 description: Form control displays a labelled input and, optionally, associated validation text and/or hint text.
 reactId: form_control
+railsIds:
+  - Primer::Alpha::FormControl
 ---
 
 import Code from '@primer/gatsby-theme-doctocat/src/components/code'