install from npm; smart-wallet / local chain only

[dckc]

• consolidates the whole page of details on installing the SDK from a git clone to one yarn create @agoric/dapp demo to install from npm packages
• replaces ag-solo style initial dapp (card store) with smart-wallet style game piece dapp running on a local chain in a docker container

refs #894, #726

rendered:

• [x] getting started

builds on:

• https://github.com/Agoric/agoric-sdk/pull/8530
  • https://github.com/Agoric/agoric-sdk/issues/3857
  • https://github.com/Agoric/agoric-sdk/issues/8380
• https://github.com/Agoric/agoric-3-proposals/issues/6
• https://github.com/agoric-labs/dapp-game-places/issues/5

related follow-on work:

• 893

• https://github.com/Agoric/agoric-sdk/pull/8537

• 889

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[dckc]

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[dckc]

we did #894 instead.

For material in this PR that wasn't covered by #894, I have moved it to separate PRs:

• 901

• 904

• 905

• 906