Add specifications to readme

[TheBeardedQuack]

Similar reason to the issue #10 I've opened. It would be best to add a list of goals that we would like to accomplish with this mod. We all know the general idea based off of the original InventoryTweaks, but what features are to be added / removed / tweaks. This can suggest something for other contributors to put their efforts to rather than running in blind.

For example, the previous mod featured sort by columns, rows, and default. As far as I can tell just by playing with the mod enabled it looks like this currently only supports default sort? Do we want to add the other? Do we not? You get the idea.

Once the initial spec list is added to the readme, others can propose new features via opening an issue or a pull request to the feature list.

[roberestarkk]

I second this. Some of my favourite features have nothing to do with sorting at all, like auto refill and Shift Clicking to move all items of a type into the other inventory.

Would love to know if support is planned for those.