Change CWS listing description files to plain text

Weblate doesn't support .lang files, so this CL changes these files to
be plain text files, since these are supported by Weblate.

Bug: twpowertools:158
Change-Id: I68f6d1aa0951992fd6071856a92bef657f46411e
diff --git a/cws/README.md b/cws/README.md
index 5e6a220..29410a9 100644
--- a/cws/README.md
+++ b/cws/README.md
@@ -4,4 +4,4 @@
 The source of truth is the [English version][1], with text in other languages
 being a translation.
 
-[1]: en/listing-description.lang
+[1]: en/listing-description.txt