blog(derived-variables): the hook and a call to action

The opening was a second-hand request; it reads better as the request every
reporting team has.  The post also ended on the docs link with nothing to do
next, so it closes with the same invitation the other recent posts use.

content/blog/derived-variables/index.md

@@ -12,7 +12,7 @@ tags:
 
 # Derived variables: computed columns you can filter on
 
-A customer asked for something simple and awkward: a column in the EDIT screen that is not in the table. A region worked out from a state code. A line value that is quantity times price. Not stored, not loaded, just *there* - and, they added, filterable.
+Every reporting team has a version of this request, and it always sounds like a five minute job: a column in the EDIT screen that is not in the table. A region worked out from a state code. A line value that is quantity times price. Not stored, not loaded, just *there* - and, as the requester usually adds, filterable.
 
 The "not stored" part is easy. The "filterable" part is where the design lives, and it is worth writing down, because it explains every other decision in the feature.
 
@@ -136,3 +136,5 @@ An expression can reference a column that is hidden from a user by [Column Level
 Derived variables ship in the next release, on SAS 9, Viya and SASjs Server. The configuration table, the settings and the post-edit validation are created by the usual upgrade - there is nothing to install beyond the release itself.
 
 The full reference, including every column of `MPE_DERIVED` and the validation rules applied at submit time, is in the [docs](https://docs.datacontroller.io/derived-variables/).
+
+If a table of yours has been waiting for "just one more column", we would love to [hear from you](/contact).