add short CONTRIBUTING.md

closes #99
closes #100

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+## Code of Conduct
+
+* Be kind to others ;
+* Critic code not people.
+
+## Code Conventions for `pure`
+
+### Public item
+
+> Namespace your item with the prefix `pure_`.
+
+* variable: `pure_my_variable`
+* function: `pure_my_public_function`
+* filename: `pure_my_public_file.fish`
+* test file: `pure_my_public_file.test.fish`
+
+### Private item
+
+> Namespace your item with the prefix `_pure_` (begin with a single underscore).
+
+* variable: `_pure_my_variable`
+* function: `_pure_my_private_function`
+* filename: `_pure_my_private_file.fish`
+* test file: `_pure_my_private_file.test.fish`
+
+### Local and Tools
+
+> No need to use namespace when your variable variable is declare locally (`set --local`) or your file/test file is related to tooling (_installer.fish_, testing package managers install).
+
+* filename: `my_tool.fish`
+* test file: `my_tool.test.fish`
+
+---
+
+We will update if other cases arise.
+
+If you are in favor of adding a `CONTRIBUTING.md`, upvote #100.