nvim: add Gentoo review-comment snippet for :=

.config/nvim/snippets/markdown.lua

@@ -18,5 +18,11 @@ return {
         name = 'quote variable',
     },
         fmt([[Please quote `${{{variable}}}`, it could contain spaces.]],
-            { variable = i(1) }))
+            { variable = i(1) })),
+    s({ trig = ':=',
+        name = 'subscribe to subslot'
+    }, {
+        t([[Very likely [needs `:=`](https://devmanual.gentoo.org/]] ..
+            [[general-concepts/slotting/index.html#abi-breakage).]]),
+    })
 }