Clarify LDK vs. rust-lightning

[moneyball]

We currently say "LDK/Rust-Lightning is a generic library which allows you to build a lightning node without needing to..." under Getting Started. I think we should do one of the following:

1. Only refer to it as LDK on the website
2. Explain what LDK is and what rust-lightning is then use them consistently on the website

[TheBlueMatt]

I think we should go with #1 - only refer to things as "LDK" unless its specifically referencing the git repo rust-lightning.

[ariard]

Same feeling, I started to be used to LDK.

[moneyball]

@ConorOkus I think we have consensus!

[ConorOkus]

This has been updated now.