Add DCO and note on how contributions are licensed

phpMyAdmin begins using a DCO as of 2013-12-01 to ensure changes are GPLv2-or-later.  Conservancy has drafted and approved the included Developer's Certificate of Origin ("DCO") and a related patch to the README to create a procedure whereby future contributors can use Signed-Off-By: in Git commits to confirm the patch is licensed under terms compatible with GPLv2-or-later.

Signed-Off-By: "Bradley M. Kuhn" <bkuhn@ebb.org>
Signed-Off-By: Tony Sebro <tony@sfconservancy.org>
Signed-Off-By: Denver Gingerich <denver@ossguy.com>
Merge remote branch 'upstream/master'
Fix 47e0223 contributor file patch submission text
Contributor file DCO text for 58f8106 per mynetx
Merge remote branch 'upstream/master'
RFE #1473 Transformation to convert Boolean value to text
- Fix coding style
- Add ChangeLog entry
Fix test for the new transformation
Update po files
Update ChangeLog for bug fixing #4157
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Translated using Weblate (Spanish)

Currently translated at 99.9% (2744 of 2744)

a translation Spanish to English was done
Initialize some variables
Merge branch 'master' of github.com:phpmyadmin/phpmyadmin
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Merge remote-tracking branch 'origin/master'
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Currently translated at 100.0% (2744 of 2744)
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Currently translated at 100.0% (2744 of 2744)
Merge pull request #768 from ossguy/master

Add DCO and note on how contributions are licensed