Fix link to getting started

Summary:
This CL fixes the internal link to the getting-started page.

# What?

Links are not relative to current position, but base URL -> ~~`fb`~~ -> `docs/fb`

Reviewed By: abesto

Differential Revision: D64040851

fbshipit-source-id: 558b0379c6f6bd2d291ad16081055070e825afeb

website/docs/README.md

@@ -51,7 +51,7 @@ $ acme --version > /dev/null
 
 ## Getting Started
 
-- [Getting Started](fb/)
+- [Getting Started](docs/fb/)
 
 
 </FbInternalOnly>