Mention JetBrains license in README.md

Jay Berkenbilt
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README.md
@@ -125,3 +125,7 @@ If the native crypto provider is in use, then, when `qpdf` detects either the Wi
 * If you use the cmake option `SKIP_OS_SECURE_RANDOM` or define the `SKIP_OS_SECURE_RANDOM` preprocessor symbol, qpdf will not attempt to use Windows cryptography or the random device.  You must either supply your own random data provider or allow use of insecure random numbers.
 * If you turn on the cmake option `USE_INSECURE_RANDOM` or define the `USE_INSECURE_RANDOM` preprocessor symbol, qpdf will try insecure random numbers if OS-provided secure random numbers are disabled.  This is not a fallback.  In order for insecure random numbers to be used, you must also disable OS secure random numbers since, otherwise, failure to find OS secure random numbers is a compile error.  The insecure random number source is stdlib's `random()` or `rand()` calls. These random numbers are not cryptography secure, but the qpdf library is fully functional using them.  Using non-secure random numbers means that it's easier in some cases to guess encryption keys.
 * In all cases, you may supply your own random data provider.  To do this, derive a class from `qpdf/RandomDataProvider` (since version 5.1.0) and call `QUtil::setRandomDataProvider` before you create any `QPDF` objects.  If you supply your own random data provider, it will always be used even if support for one of the other random data providers is compiled in.  If you wish to avoid any possibility of your build of qpdf from using anything but a user-supplied random data provider, you can define `SKIP_OS_SECURE_RANDOM` and not `USE_INSECURE_RANDOM`.  In this case, qpdf will throw a runtime error if any attempt is made to generate random numbers and no random data provider has been supplied.
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+# Acknowledgments
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+The qpdf project has a JetBrains license through their [Open Source Program](https://www.jetbrains.com/community/opensource/#support). We are grateful for this program and have been enjoying the befits of their high-quality products.