Update reference to "Standard Library" and what it is made up of

Might consider updating this. It says that core and vendor folders constitute the implementation code and bindings for the std lib.

Probably written before you split out Base.

The question of what Odin's std lib is (or is not) seems to reoccur.

Latest from Odin's creator that explains what the Standard Lib is or is not: https://discord.com/channels/568138951836172421/585077163250941962/1268998964993196042

https://odin-lang.org/docs/overview/#what-to-do-if-you-get-stuck