sql: add comment to explain sql-indent config

layers/+lang/sql/packages.el

@@ -13,6 +13,11 @@
       '(
         company
         sql
+        ;; This mode is more up-to-date than the MELPA one.
+        ;; Turns out that it is available in GNU ELPA but we cannot
+        ;; force Spacemacs to fetch from it for now, it will always
+        ;; pickup the MELPA version. So for now we use an explicit
+        ;; recip to fetch from GitHUb the package.
         (sql-indent :location (recipe
                                :fetcher github
                                :repo "alex-hhh/emacs-sql-indent"