Add guide for migrating to v3.0.0

Migrating to v3.0.0.md

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+Text-Based Actors v3.0.0 ships with some breaking changes that might affect macros
+or custom sheets within your world. This page will go over what those breaking
+changes are, and what you can do to restore functionality.
+
+**If you did not write any custom Macros or world scripts, you do not need to
+make any changes!**
+
+## API Location Change
+The easiest breaking change to fix, is that the globally available `taf` constant
+now contains multiple subsections. Wherever you used `taf` previously, can be
+directly replaced with `taf.api`. As there is now a `taf.config` as well, which
+contains all of the code-configurable properties of the system.
+
+You can read more about how stuff was moved in [this issue](https://git.varify.ca/Foundry/taf/issues/50)
+
+## Actor Attributes into Attribute Items
+Attributes used to exist in the Actor using the following format:
+```js
+system: {
+	attr: {
+		attr_key: {
+			name: "Attr Key",
+			value: 0,
+			max: 5,
+			isRange: true,
+		}
+	}
+}
+```
+however Attributes are now stored as an Item subtype. A one-time migration will
+be performed on all world and compendium actors that have attributes in order to
+convert them into the item subtypes. However this does not affect any macros or
+other shortcuts for creating Actors that you may have. What you should do while
+creating Actors programmatically now is to provide an `items` array with the
+required minimum-attribute-item data that you desire. There is no automatic
+migration from creating/updating actors in the old style to the embedded items.
+
+There is a short-cut for updating these attributes on the Actor though by doing
+something similar to:
+```js
+let actor = game.actors.getName(`Frankie`);
+await actor.setAttributeValue("strength", 20);
+```
+Which will update the "strength" attribute on the actor named "Frankie" to 20,
+if that attribute cannot be found, it will do nothing.