add CONTRIBUTING.md

Signed-off-by: Mattéo Rossillol‑‑Laruelle <[email protected]>

Author: beatussum

CONTRIBUTING.md

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+# Contributing to Beatussum's Gentoo overlay
+
+First, thanks for wanting to contribute to my overlay.
+
+## Table of contents
+
+- [Table of contents](#table-of-contents)
+- [How to contribute?](#how-to-contribute)
+    - [General guidelines](#general-guidelines)
+    - [What is specific to this overlay](#what-is-specific-to-this-overlay)
+        - [Documentation files](#documentation-files)
+        - [EAPI](#eapi)
+        - [Ebuilds without test](#ebuilds-without-test)
+        - [Extra variables](#extra-variables)
+        - [Keywords](#keywords)
+        - [Live ebuilds](#live-ebuilds)
+        - [Metadata file](#metadata-file)
+        - [Non-binary packages](#non-binary-packages)
+        - [Package removal](#package-removal)
+        - [Patch files](#patch-files)
+        - [Prebuilt packages](#prebuilt-packages)
+        - [Version bumps](#version-bumps)
+
+## How to contribute?
+
+### General guidelines
+
+This overlay respects the same rules and coding styles as [the main Gentoo repository](https://github.com/gentoo/gentoo/).
+It is recommended therefore to consult the section _Maintain ebuilds_ of [the page _Contribute to Gentoo_](https://www.gentoo.org/get-involved/contribute/); in particular, the following pages must be read
+
+- [Basic guide to writing ebuilds](https://wiki.gentoo.org/wiki/Basic_guide_to_write_Gentoo_Ebuilds),
+- and [The Gentoo Developer Manual](https://devmanual.gentoo.org/).
+
+### What is specific to this overlay?
+
+#### Documentation files
+
+All documentation files should be included.
+If some files need additionnal build process, they should be added only when the `doc` USE flag enabled.
+
+#### EAPI
+
+Only `EAPI=8` is allowed.
+
+#### Ebuilds without test
+
+If an ebuild does not have test, it should specify `RESTRICT="test"`.
+
+#### Extra variables
+
+Variable should be written using [snake case](https://en.wikipedia.org/wiki/Snake_case).
+
+Extra variable defined as global variable should be uppercase.
+If this variable _override_ an other variable among [these ones](https://devmanual.gentoo.org/ebuild-writing/variables/), it should be prefixed by `MY_`, e.g. `MY_PN="${PN^^}"`.
+
+Local variable should be lowercase and be declared as `local`, e.g. `local my_local_variable`.
+
+#### Keywords
+
+Only [AMD64](https://fr.wikipedia.org/wiki/AMD64) is supported in this overlay, i.e. `KEYWORDS="~amd64"` or `RESTRICT="-* ~amd64"`.
+
+#### Live ebuilds
+
+If you want to provide a live version of an ebuild, it is recommended to have the same ebuild for the latest version and the live one with the following pattern:
+
+```ebuild
+if [[ "${PV}" = 9999 ]]; then
+    inherit git-r3
+    EGIT_REPO_URI="<git URI>"
+else
+    SRC_URI="<src URI>"
+    KEYWORDS="~amd64"
+fi
+```
+
+`9999` must be replaced by the appropriate format, e.g. the live version of an ebuild with the version `19700101` should be `99999999`.
+
+#### Metadata file
+
+The metadata file should provide as many elements as possible, in particular, `<upstream>` should be as complete as possible.
+
+#### Non-binary packages
+
+If a package does not include binary files, the ebuild should include `RESTRICT="binchecks test"` and `<stabilize-allarches/>` in the metadata.xml file.
+
+#### Package removal
+
+If a package need to be removed, it has to be masked **15 days** before.
+
+#### Patch files
+
+Patch files should be created with `git format-patch`.
+
+#### Prebuilt packages
+
+Prebuilt packages should include in their ebuild `QA_PREBUILT` and, according to the redistribution rules, `RESTRICT="bindist mirror"`.
+
+#### Version bumps
+
+Versions bumps or rebumps should replace the previous version for the current `SLOT`.