[fix] Minor doc touchups re. QR encode (#6861)

Cf. <https://github.com/koreader/koreader/pull/6844#issuecomment-723672448>.

doc/config.ld

@@ -24,6 +24,7 @@ file = {
     '../base/ffi',
     '../platform/android/luajit-launcher/assets',
     exclude = {'../base/ffi/sha2.lua',
+        '../base/ffi/qrencode.lua',
         '../plugins/evernote.koplugin/slt2.lua',
         '../plugins/newsdownloader.koplugin/lib/handler.lua',
         '../plugins/newsdownloader.koplugin/lib/xml.lua',

plugins/qrclipboard.koplugin/main.lua

@@ -1,5 +1,7 @@
 --[[--
 This plugin generates a QR code from clipboard content.
+
+@module koplugin.QRClipboard
 --]]--
 
 local Device = require("device")