📝 docs:Add base folder README file

src/base/README.md

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+# Base
+
+The **base** folder contains the stylistic foundations of the graphic charter. It includes definitions of the _colors_ and _fonts_ used consistently in interface design.
+This folder is made up of two subfolders:
+- colors
+- fonts
+
+## Colors
+
+This subfolder contains the `SCSS` files defining the project's color palettes. Each file represents a specific color from the graphic charter.
+
+## Fonts
+
+This subfolder contains the project's typographic definitions, in accordance with the graphic charter. It also includes a folder dedicated to the Spectral font, with SCSS files defining :
+
+- the font family
+- sizes
+- line heights
+- weights