Documentation of esp-hal once unified

[MabezDev]

READMEs

• Update README to match with unification changes #1217
• Update esp-hal/README #1228
• Initial version of README.md for the examples package #1237

lib docs

• Update the checklist in the PR template #1242
  • JB: This can probably wait until post-release?
• Update the CONTRIBUTING.md guide #1225
  • JB: See above

external

• Book updates #1218
• Use new esp-hal package instead of chip-specific HAL packages once published esp-template#148
• Migration guide for updating to esp-hal@0.16.x #1222
• no_std training #1220

[JurajSadel]

I'm going to start with READMEs

[jessebraham]

I've moved some of the documentation tasks to a separate issue: #1221

[jessebraham]

Fleshed out examples/README.md in #1237

[jessebraham]

READMEs have been updated.

[jessebraham]

@MabezDev @bjoernQ what are your thoughts on delaying the remaining few points here, in the interest of getting the release out? I think it's fine if we tackle them post-release, personally.

All remaining tasks have their own issues open, so maybe this can be closed.

[MabezDev]

Sounds good.