[#61] add contributing info

CONTRIBUTING.md

@@ -0,0 +1,40 @@
+# Contributing
+
+### With issues:
+
++ Use the search tool before opening a new issue.
++ Please provide source code and commit sha (optional) if you found a bug.
++ Review existing issues and provide feedback or react to them.
+
+###  With pull requests:
+
++ Open your pull request against `dev` branch.
+
+  a) The pull request name format should correspond to format
+    ```
+    [#<issue reference>] <pull request name>
+    ```
+  Example  
+    ```
+    [#61] add `CONTRIBUTING.md`
+    ```
+  b) The pull request branch should contains tag (`bugfix`, `feature`, etc.) and correspond to format
+    ```
+    <tag>/<issue reference>_<additional description if required>
+    ```
+  Example
+    ```
+    feature/61_contributing_info
+    ```
+  c) The commit message should correspond to format
+    ```
+    [#<issue reference>] <commit message>
+    ```
+  Example
+    ```
+    [#61] add contributing info
+    ```
++ Pull request should have no more than **one** commits, if not you should squash them.
++ It should pass all tests in the available continuous integration systems such as GitHub Actions.
++ Pull request should contain tests (added/modified) to cover your proposed code changes.
++ If pull request contains a new feature, all information about feature must be described in `README.md`.