Adds initial test framework; adds PrivateKey.from_nsec() (#13)

* Adds initial test framework; adds PrivateKey.from_nsec()

* Update setup.py

test/README.md

@@ -0,0 +1,31 @@
+# Testing python-nostr
+
+## Set up the test environment
+
+Install the test-runner dependencies:
+```
+pip3 install -r test/requirements.txt
+```
+
+Then make the `nostr` python module visible/importable to the tests by installing the local dev dir as an editable module:
+```
+# from the repo root
+pip3 install -e .
+```
+
+## Running the test suite
+Run the whole test suite:
+```
+# from the repo root
+pytest
+```
+
+Run a specific test file:
+```
+pytest test/test_this_file.py
+```
+
+Run a specific test:
+```
+pytest test/test_this_file.py::test_this_specific_test
+```