Fixes cantonbecker#28

Update the README to use the long GPG key id `0x9277AD7136E1D9B6` instead of the short key id `36E1D9B6`.

* Add a new section providing instructions on how to use GPG for signing and verifying files.
* Include detailed instructions on how to download and verify the code from GitHub.
* Provide guidance on how to generate wallets securely using the downloaded code.
* Add a section on troubleshooting common issues that users might encounter.
* Include a FAQ section to address frequently asked questions.
* Explain the purpose of the `.sig` file and its role in verifying the integrity and authenticity of the `generate-wallet.html` file.

Update `images/ubuntumono-b-webfont.svg` to ensure the SVG content is correctly placed in the file.

Add `.devcontainer/devcontainer.json` with a task to launch a Python HTTP server.

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