wrote intro docs, promised a tutorial

docs/intro.rst

@@ -2,4 +2,67 @@
 Introduction
 ============
 
-todo
+ASAP-Stereo (Ames Stereo Automated Pipeline) is a Python API
+that orchestrates the NASA Ames Stereo Pipeline (ASP_) for HiRISE and CTX stereo image processing. 
+ASAP implements functions that use various command-line tools from GDAL, ASP, and USGS ISIS to 
+produce Digital Elevation Models (DEMs) following a workflow of steps described by
+Mayer and Kite 2016 in their tool asp_scripts_. 
+The workflows generally follow a procedure of first downloading and calibrating the data, 
+producing stereo products using ASP, and then finally aligning the stereo products with 
+reference elevation data and the geoid. The commonality in workflow procedures and the
+number of steps involved mean that users will significantly benefit from the workflow's 
+automation. ASAP also provides both a command-line interface for the whole API 
+and Jupyter Notebooks, accessible through the command-line interface, that executes the workflows 
+for CTX and HiRISE (described below). By providing all three interfaces, users can execute workflows,
+and then re-run individual steps to improve stereo product quality and 
+run the ASAP workflows in a semi-automatic fashion. 
+
+.. _asp_scripts: https://github.com/USGS-Astrogeology/asp_scripts
+.. _ASP: https://github.com/NeoGeographyToolkit/StereoPipeline
+
+ASAP Core Functionality
+-----------------------
+ASAP uses the sh_ python library to access external command-line tools 
+as if they were Python functions without any direct subprocess management code in ASAP.
+Although using Python to call other subprocesses is not new, 
+the sh project makes it remarkably easy to do this with minimal code.
+Using sh enables ASAP to reuse existing command-line tools 
+and to use Python for tasks it is best suited. 
+
+.. _sh: https://github.com/amoffat/sh
+
+
+ASAP's Commandline Interface (CLI)
+----------------------------------
+
+ASAP's CLI is automatically created from the Python classes
+and functions using the python-fire_ project,
+requiring no code changes to the Python API.
+Python-fire allows ASAP to simultaneously provide both the 
+API and CLI with no additional code to maintain.
+For example, using python-fire, it is possible to enable tab-completion
+for ASAP's CLI or drop into interactive python sessions. 
+The python-fire_ GitHub page is an excellent resource to 
+learn more about the project. 
+
+.. _python-fire: https://github.com/google/python-fire
+
+
+ASAP Jupyter Notebook Workflows
+-------------------------------
+
+ASAP provides Jupyter Notebook template workflows to users,
+and they are the easiest way to use ASAP. 
+ASAP uses the Papermill_ project to execute the notebook workflows, 
+that project can turn any Jupyter Notebook into a parameterized command-line tool.
+Papermill uses the workflows provided by ASAP as templates
+that are then updated to use the user's specified images and parameters.
+When executed, the notebooks capture all the logs from the various steps 
+of ASAP and the underlying tools into the notebook file. 
+In addition to the logs, the notebooks also include images generated during 
+the workflow's steps for quick quality inspection by the user.
+Users can share notebooks, allowing for reproducibility and traceability in their scientific data.
+More details about the notebook workflows will be provided in the tutorials section of the documentation.
+
+
+.. _Papermill: https://github.com/nteract/papermill