Add README

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

README.md

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+# AGES - Adventure Game Engine, Stupid
+
+This is a dumb little text adventure game engine I'm working on.
+
+You can try out the example game by running:
+
+`python -m agame examplegame`
+
+I believe this requires only Python 3.6, but was written in Python 3.9. Tread
+with some caution.
+
+# Concepts
+
+**Actions** are at the heart of the engine. These display things (such as the
+`PrintAction`), as well as change the state of the game (such as
+`TeleportAction` and `RevealItemAction`). They are invoked by triggers,
+described below.
+
+**Triggers** are what drive the game, and turn human input into actions that are
+executed. They are responsible for parsing input, and executing actions based on
+input and game state. Items in a game have a mapping of the triggers that can
+activate a list of actions.
+
+**Items** are what carry the behavior of actions, and what triggers look for to
+activate themselves. Items have descriptions for how they should be announced in
+the room, plus the actions for appropriate actions. Triggers will also use the
+list of synonyms provided by items to identify them.
+
+**ItemInsts** are instances of items. Usually when you're dealing with items,
+you're actually dealing with an `ItemInst`. An `Item`is stored in the game
+database, while an `ItemInst` is used in rooms and the player's inventory.
+
+**Rooms** hold sets of items. The player is present in only one room at a time;
+this is mostly an organizational tool for locations in a game.
+
+**Variables** are a simple string->value mapping held in the game's database.
+
+The **database** is a single source of information for the game to use. The
+database contains all items, triggers, rooms, and variables that are used in the
+game. The database is *not* immutable; the rooms and variables in the database
+are expected to be altered at runtime. (Maybe this should change, although I
+don't feel like doing so right now.)