initial README

Author: jairomelo

README.md

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+# Unlocking Data. A Gentle Introduction to APIs
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+This repository contains the source code for the book "Unlocking Data. A Gentle Introduction to APIs".
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+The book is built with [Quarto](https://quarto.org/) and relies heavily on [Observable JS](https://quarto.org/docs/interactive/ojs/).
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+
+## How to publish the book
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+Because we require API keys to run the examples, the book is build using [Github Actions](https://quarto.org/docs/publishing/github-pages.html#github-action). If the repository is fork, be sure to set the API keys in the Github Actions secrets. See `_environment.required` file to know which API keys are required to make the examples work.
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+Publications are done using the `.github/workflows/publish.yml` file, which is triggered by a push to the `main` branch, and deploy the book to the `gh-pages` branch. The `gh-pages` branch must exist before the first publication and be set as the branch to build and deploy your Github Pages site.
+
+We opt for execute the code as part of a Github Action, because it allows us to fetch the data from external sources. Updated computations are still stored in `_freeze` folder, and it's recommended using a Python virtual environment to run Quarto and install the required packages using `requirements.txt` file.
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