Update README.md

sources/README.md

 # Sources
-## File types
+## File types used for sources
 * *.doc, +.docx  = Microsoft Word 2010
 * *.mmap = Corel/Mindjet Mindmanager 2019
 * *.pptx = Microsoft Powerpoint 2010
-## Conversion
+## Conversion from source files to workshop-kit files 
 * From *.doc or *.docx to *.pdf: MS-Word / Microsoft Print to PDF 
 * From *.pptx to *.pdf: MS-Powerpoint: Microsoft Print to PDF
 * From *.mmap to *.html: Mindmanager / Export to HTML5 Interactive Map (and distribute the file) or Publish to Mindmanager cloud (and distribute the hyperlink)
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