Adding to Readme (tardis-sn#181)

* Added MARCS_TEST_FPATH, removed redundancies

* Use model fixture in all tests

* Combined all marcs tests

* Add relevant links to README file

* Add correct hyperlinks and clearer language

* Add whitespace before license

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Co-authored-by: Hayden James Monk <[email protected]>

README.rst

@@ -1,6 +1,14 @@
 STARDIS Stellar Radiative transfer
 ----------------------------------
 
+Welcome to STARDIS!
+STARDIS is an LTE radiative transfer Python package that utilizes the TARDIS infrastructure 
+to generate synthetic stellar spectra. For more information about STARDIS, 
+including a quickstart notebook, physics walkthrough and installation instructions, go to our `documentation page <https://tardis-sn.github.io/stardis/>`_. 
+Or, try running the `quickstart notebook <docs/quickstart/quickstart.ipynb>`_ yourself!
+
+To learn more about TARDIS, including documentation and collaborator information, go `here <https://tardis-sn.github.io/tardis/>`_.
+
 License
 -------