docs: update top level README and remove unused legacy files

[b-cooper]

Changelog

• remove old architecture_and_planning writeup that is no longer accurate and otherwise covered by the newer CONTRIBUTING.md
• remove monorepo copy of audio speaker test, as it is built into BR
• remove unused .dockerignore
• update top level README.md copy for accuracy
• add PD to top level README.md

[codecov]

Codecov Report

Merging #4717 into edge will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             edge    #4717      +/-   ##
==========================================
+ Coverage   58.05%   58.13%   +0.08%     
==========================================
  Files         955      958       +3     
  Lines       26254    26831     +577     
==========================================
+ Hits        15242    15599     +357     
- Misses      11012    11232     +220

Impacted Files	Coverage Δ
opentrons/server/http.py	92.53% <0%> (-0.45%)	⬇️
...l-designer/src/top-selectors/tip-contents/index.js	0% <0%> (ø)	⬆️
...tocol-designer/src/components/steplist/StepItem.js	0% <0%> (ø)	⬆️
.../RobotSettings/UpdateBuildroot/SyncRobotMessage.js	0% <0%> (ø)	⬆️
protocol-designer/src/top-selectors/substeps.js	0% <0%> (ø)	⬆️
...c/components/StepEditForm/forms/TemperatureForm.js	0% <0%> (ø)	⬆️
...col-designer/src/components/DeckSetup/DeckSetup.js	0% <0%> (ø)	⬆️
...col-designer/src/components/DeckSetup/ModuleTag.js	0% <0%> (ø)	⬆️
...tocol-designer/src/top-selectors/timelineFrames.js	15.78% <0%> (ø)
...esigner/src/components/steplist/MagnetStepItems.js	0% <0%> (ø)
... and 14 more

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[btmorr]

Looks good. Thanks for keeping this cleaned up

[IanLondon]

🚢 🌊 🎵

[mcous]

LGTM! I've got a couple tiny edit requests if we want them