chore: expanded the README

README.md

@@ -1 +1,37 @@
 # FTB Filter System
+
+## Overview
+
+FTB Filter System (aka FFS) is a powerful item filtering mod with friendly GUI editing. It doesn't do much on its own,
+but is intended to be used by other mods which need to filter items; FTB Quests in particular, but it offers an API
+which any mod can use.
+
+## Using FFS
+
+FFS adds a single item, the **Smart Filter**. All configuration is done via this item, by simply right-clicking it.
+This opens a GUI, with a list which initially contains just a "Root" element, and "Add" / "Delete" / "Configure" buttons
+on the right:
+
+* Click "Add..." to pop up a list of available subfilters which you can add. 
+  * On the left side of the list are **compound** filters, to which more filters can be added as children, forming a filter hierarchy.
+  * On the right side (in possibly multiple columns) are **basic** filters, which do actual matching against items.
+  * All the filter buttons have a tooltip with a brief explanation of what they do (should be obvious in general)
+* Click "Delete" to delete the currently-selected filter.
+  * Deleting a compound filter also deletes all its children
+* Click "Configure..." to pop up another screen allowing the currently-selected filter to be configured
+  * Not all filters can be configured; compound filters don't have any configuration, and some basic filters don't either
+  * You can also double-click any filter in the list to open its configuration screen
+
+At the bottom are "Done" and "Cancel" buttons:
+* Click "Done" to save any changes you've made to the filter
+* Click "Cancel" (or press Escape) to discard any changes (you will be prompted to confirm discarding unsaved changes)
+
+Other tips and tricks:
+* Some filters allow dragging of items from JEI to configure them: the Item Filter, the NBT and Fuzzy NBT filters, and the Mod filter
+* Filters can be dragged in the list to move them around in the filter hierarchy, subject to the following rules:
+  * The Root filter can never be moved
+  * Filters can only be dragged onto compound filters
+  * Compound filters can only be dragged onto filters at the same level or higher up in the hierarchy (dragging a filter into its own child isn't a very sane thing to do...)
+* You can quickly test if a filter matches what it's supposed to:
+  * Hold the configured filter in your main hand, and the item to be tested in your offhand
+  * Then sneak-right-click the filter and you'll get a chat response indicating a match success or failure