update and relocate CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,56 @@
+Hi reader!
+
+If you ended here then you probably want to contribute to this project: thanks for that!
+
+In order to have your contribution more easily integrated please respect the following rules:
+
+## Reporting an issue
+
+This project uses GitHub issues to manage the issues. Open an issue directly in GitHub.
+Use the provided issue template when submitting a new issue and as much as possible provide a reproducible example.
+
+## Building master
+
+Building the project is as simple as:
+
+```
+git clone [email protected]:jgitver/jgitver-maven-plugin.git
+cd jgitver-maven-plugin
+./mvnw package
+```
+
+## Contribution rules
+
+1. contributions are provided by pull-request only (no email, or anything else)
+1. before submitting your pull-request you have successfully run a local build using the following command
+    - `mvn -Prun-its clean install`
+1. if your contribution consist in some code modification then your change is covered by a unit or integration test
+    - _for documentation only contribution, this requirement can be omitted)_
+1. you have kept several commits in your PR only if those commits are relevant ; for typos commits or like please squash them.
+
+
+### IDE Config and Code Style
+
+jgitver has a strictly enforced code style using [google-java-format](https://github.com/google/google-java-format). Code formatting is checked during the build phase by the [spotless-maven-plugin](https://github.com/diffplug/spotless/tree/master/plugin-maven#google-java-format).
+
+If you want to run the formatting without doing a full build, you can run `mvn spotless:apply`.
+
+#### Eclipse Setup
+
+Follow instructions from [google-java-format](https://github.com/google/google-java-format#eclipse) site.
+
+> The eclipse plugin is outdated and uses the old `1.6` version of google-java-format _(see also [google-java-format#331](https://github.com/google/google-java-format/issues/331))_.  
+> You can manually apply the styling by running: `mvn spotless:apply`
+
+#### Intellij Setup
+
+Follow instructions from [google-java-format](https://github.com/google/google-java-format#intellij-android-studio-and-other-jetbrains-ides) site.
+
+### Integration warning
+
+As we want to keep the project clean, __every commit__ in any branch (expect master & maintenance branches) can be __rewritten__.
+
+From the last sentence we give 2 advices:
+
+- initiate your PR from a branch in your fork and not from the master. When your PR will be integrated, it can be modified & adapted leading your fork with a master branch that as diverged from upstream
+- do not initiate work in your fork from a PR that could be rewritten

README.md

@@ -246,6 +246,8 @@ Think to modify your IDE settings regarding maven version ; if required do not u
 
 ## Build & release
 
+see also the [Contributing guide](CONTRIBUTING.md).
+
 ### Github Markdown rendering
 
 Before pushing try to always verify that the modifications pushed in MD files will be correctly rendered by Github.