MDL-57972 javascript: add upgrade instructions for truncate.js

Part of MDL-55611

lib/amd/src/truncate.js

@@ -13,6 +13,14 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
+/**
+ * Description of import/upgrade into Moodle:
+ * 1.) Download from https://github.com/pathable/truncate
+ * 2.) Copy jquery.truncate.js into lib/amd/src/truncate.js
+ * 3.) Edit truncate.js to return the $.truncate function as truncate
+ * 4.) Apply Moodle changes from git commit 7172b33e241c4d42cff01f78bf8570408f43fdc2
+ */
+
 /**
  * Module for text truncation.
  *