html-manipulations/addSummary.js: rename and document to reflect better what it does

html-manipulations/addSummary.js

@@ -1,3 +1,5 @@
+//looks for an html comment pattern, and, if found,
+//adds the text before it to the doc under the key `summary`.
 const reg = /^(?<summary>.+)?<!--summary-above-->/s
 export default (doc) => {
   const result = reg.exec(doc._body);

pipeline.ori

@@ -45,7 +45,7 @@
   and ends up in a separate field of the document.
   So we dont have to worry about the title being part of the summary.
   */
-  withSummary: Tree.map(asHtml, ./html-manipulations/extractSummary.js)
+  withSummary: Tree.map(asHtml, ./html-manipulations/addSummary.js)
 
   /*
   Removing private content coming below the html paragraph `<p>—private-below—</p>`