Add issue link for introspecting select

Hi, wonderful Bazelers,

I was reading these docs and found myself looking for the relevant issue for select introspection. Since it took a bit of finding, I thought I'd propose adding a link to the issue to save time for future readers. Hopefully, that'll also help people subscribe to updates.

Cheers!
Chris
(ex-Googler)

Closes bazelbuild#16824.

PiperOrigin-RevId: 491303661
Change-Id: Idf9cca39f8e7ddbeb635dd53b811cf4d7b7e6f59

site/en/docs/configurable-attributes.md

@@ -862,7 +862,7 @@ Macros [can't](#faq-select-macro) evaluate select(s) because macros evaluate bef
 Bazel knows what the build's command line parameters are. Can they at least read
 the `select()`'s dictionary to, for example, add a suffix to each value?
 
-Conceptually this is possible, but it isn't yet a Bazel feature.
+Conceptually this is possible, but [it isn't yet a Bazel feature](https://github.com/bazelbuild/bazel/issues/8419).
 What you *can* do today is prepare a straight dictionary, then feed it into a
 `select()`: