Update README.md

Added details of documents in repo.

Author: delphidabbler

README.md

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 # delphi-tips
-A bunch of Delphi language tips migrated from the DelphiDabbler.com webiste, plus others
+
+This is a bunch of Delphi language tips migrated from the DelphiDabbler.com webiste, plus some others.
+
+The tips from DelphiDabbler.com are in the `tips` folder. There is one PDF file for each tip. The files are named with the title of the tip, or an approximation of it.
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+The additional tips are in the `extra` folder. There are two open document format documents. One contains a large number of tips downloaded from the former _Delphi Pool_ website. The second contains tips collected online by _"topellina"_. There may be some duplication of tips between the PDF files and these documents. Conversely, some tips that appear in the PDFs may have been sourced and deleted from these files.
+
+Bear in mind that all the tips are old now. Very few of the tips in the `tips` folder and none of those in the `extra` folder have been tested. **Use with care and at your own risk!**