Document how to update bindings

[tjkirch]

I'd be up for helping update crankstart to SDK 1.13.0, and I might be able to muddle my way through, but docs would certainly help!

[rtsuk]

1. Install the bindgen-cli and its dependencies.
2. Have the PlayDate SDK installed at $HOME/Developer/PlaydateSDK.
3. Run ./scripts/generate_bindings.sh from the crankstart directory.

As far as I know, this has only every been run on a Mac.

[rtsuk]

I went through these steps to make sure they were the right ones and it worked so I'm going to push the new bindings.

[tjkirch]

Awesome, thanks! I might take a look to see how it works on Linux, too.

[rtsuk]

I set this up kinda wrong. I'm not sure the entire target triple is needed, probably just the processor family. That way AArch64 Linux or Mac could use the same bindings.

[tjkirch]

I tried this today because I wanted to update to SDK 1.13.6, which has a change to the signature of draw_text. A few notes:

• I had to install zsh to run generate_bindings.sh; it seems like a simple enough script to convert to sh so it wouldn't require this, if you wouldn't mind. I'll try it.
• Setting PLAYDATE_SDK_PATH works instead of having the SDK at a specific location, thanks to this.
• I had to install glibc-devel-32bit (on Void Linux, from the multilib repo) to get stubs-32.h.
• I had to add an include directory for the device invocation of bindgen. I'll do a PR. [edit: see #42]

In the end, it didn't find any changes from the existing bindings. The C API didn't change, only Lua. I should have checked that first ;(

In terms of actually closing this issue by documenting the process - I guess it could just go at the bottom of the README, unless you'd prefer a new document? I can try it.

[rtsuk]

Bottom of the readme is fine.

I'll have to check it on Mac after you modify it.