Initial project import

tools/v/vlib/builtin/README.md

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+## Description
+
+`builtin` is a module that is implicitly imported by every V program.
+
+It implements the builtin V types `array`, `string`, `map`.
+It also includes Unicode-aware string helpers such as `string.graphemes()`
+for splitting text into grapheme clusters.
+
+It also implements builtin functions like `println`, `eprintln`, `malloc`,
+`panic`, `print_backtrace`.
+
+The autogenerated documentation for `builtin` functions is lacking, so for these
+functions, please refer to the
+[official V documentation](https://github.com/vlang/v/blob/master/doc/docs.md).