refresh front-page README. still need to take new GIFs

README.md

@@ -4,14 +4,66 @@ Ever been on a bus stuck in traffic, wondering why there are cars parked on the
 road instead of a bus lane? A/B Street is a game exploring how small changes to
 a city affect the movement of drivers, cyclists, transit users, and pedestrians.
 
-- [Game features](docs/articles/features/article.md)
-- [Instructions to run the game](docs/INSTRUCTIONS.md)
+[Play A/B Street on Windows, Mac, Linux](docs/INSTRUCTIONS.md)
 
 ![demo](docs/articles/features/screenshots/demo.gif)
 
+## Features
+
+More details [here](docs/articles/features/article.md).
+
+- The map
+  - A detailed rendering of Seattle from OpenStreetMap and King County GIS data,
+    including sidewalks, on-street parking, bike lanes, bus-only lanes, turn
+    lanes, buildings, and bus stops.
+  - Intersections governed by stop signs and traffic signals, with default
+    signal timings heuristically inferred. Hand-tuned geometry to reasonably
+    model Seattle's strangest intersections.
+  - You can adjust lane types, stop signs, and traffic signals.
+- The traffic
+  - Individual cars, buses, bikes, and pedestrians move through the map.
+  - Most trips are multi-modal -- for example, a pedestrian exits a building,
+    walks a few blocks over to their parked car, drives somewhere, looks for
+    parking, and walks to their final destination.
+  - A realistic set of trips -- how many people go from building 1 to building 2
+    at some time using some form of transport -- comes from
+    [PSRC's Soundcast](https://www.psrc.org/activity-based-travel-model-soundcast)
+    model.
+- The gameplay
+  - Start in sandbox mode, exploring the map, watching traffic patterns,
+    following individual agents, looking for problems.
+  - Jump to edit mode, where you can convert some on-street parking to bus lanes
+    and adjust traffic signals to try to fix some problem.
+  - Try your change in A/B test mode, running two traffic simulations
+    side-by-side. Explore how individual agents finish their trips faster or
+    slower, and compare aggregate results about different groups of traffic.
+
+## Project mission
+
+If you fix some traffic problem while playing A/B Street, my ultimate goal is
+for your changes to become a real proposal for adjusting Seattle's
+infrastructure. A/B Street is of course a game, using a simplified approach to
+traffic modeling, so city governments still have to evaluate proposals using
+their existing methods. A/B Street is intended as a conversation starter and
+tool to communicate ideas with interactive visualizations.
+
+Why not leave city planning to professionals? People are local experts on the
+small slice of the city they interact with daily -- the one left turn lane that
+always backs up or a certain set of poorly timed walk signals.
+[Laura Adler](http://www.govtech.com/data/SimCities-Can-City-Planning-Mistakes-Be-Avoided-Through-Data-Driven-Simulations.html)
+writes:
+
+> "Only with simple, accessible simulation programs can citizens become active
+> generators of their own urban visions, not just passive recipients of options
+> laid out by government officials."
+
+Existing urban planning software is either proprietary or hard to use. A/B
+Street strives set the accessible bar high, by being a fun, engaging game.
+
 ## Contributing
 
-If you're skilled in user experience design, traffic simulation, data
-visualization, or government outreach, please contact Dustin Carlino at
+I'm a one-person team. If you want to bring this to your city or if you're
+skilled in user experience design, traffic simulation, data visualization, or
+civic/government outreach, please contact Dustin Carlino at
 <dabreegster@gmail.com>. I also welcome any contributions on
 [Patreon](https://www.patreon.com/abstreet).

docs/INSTRUCTIONS.md

@@ -69,4 +69,5 @@ A/B Street binary releases contain pre-built maps that combine data from:
 - https://github.com/seattleio/seattle-boundaries-data
   (https://creativecommons.org/publicdomain/zero/1.0/)
 - DejaVuSans.ttf (https://dejavu-fonts.github.io/License.html)
-- Puget Sound Regional Council (https://www.psrc.org/activity-based-travel-model-soundcast)
+- Puget Sound Regional Council
+  (https://www.psrc.org/activity-based-travel-model-soundcast)