Update docs

This is a smaller PR that makes some aspects of the docs more apparent but, per discussion, doesn't mark individual wallet adapters as deprecated.

 - State what wallet adapter an wallet standard are in the README
 - Mention pnpm 8 requirement explicitly (I'm relatively sure pnpm 7 won't work)
 - Make Ster Projects more prominent by moving it before the long list of individual wallet adapters
 - Make demo and demo code more prominent in README
 - Use relative links wherever possible (which keeps links working across forks and looks neater)
 - Use a neater syntax so the markdown is viewable in terminal, VScode, and other apps that do not render markdown.

Author: mikemaccana

Diff for: BUILD.md

@@ -3,7 +3,7 @@
 ### 0. Prerequisites
 
 * Node 16+
-* PNPM
+* PNPM 8
 
 If you have Node 16+, you can [activate PNPM with Corepack](https://pnpm.io/installation#using-corepack):
 ```shell