Create UsingTestPyPI.md (#1061)

Author: axelsrz

UsingTestPyPI.md

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+# Using TestPyPI to consume rc builds
+The BotBuilder SDK rc build feed is found on [TestPyPI](https://test.pypi.org/). 
+
+The daily builds will be available soon through the mentioned feed as well.
+
+
+# Configure TestPyPI
+
+You can tell pip to download packages from TestPyPI instead of PyPI by specifying the --index-url flag (in the example below, replace 'botbuilder-core' for the name of the library you want to install)
+
+```bash
+$ pip install --index-url https://test.pypi.org/simple/ botbuilder-core
+```
+If you want to allow pip to also pull other packages from PyPI you can specify --extra-index-url to point to PyPI.
+This is useful when the package you’re testing has dependencies:
+
+```bash
+pip install --index-url https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ botbuilder-core
+```