[DOC] Updated readme and contributing files (bp #1284) (#1294)

* [DOC] Updated readme and contributing files (#1284)

* Updated readme and contributing files

(cherry picked from commit 6a64398)

# Conflicts:
#	README.md

* Update README.md

Fix merge conflicts in README

* Added pics for README

Co-authored-by: Ekaterina Mekhnetsova <[email protected]>
Co-authored-by: Ekaterina Mekhnetsova <[email protected]>

CONTRIBUTING.md

@@ -16,17 +16,28 @@
 *******************************************************************************/-->
 
 # How to Contribute
-We welcome community contributions to Intel(R) oneAPI Data Analytics Library. If you have an idea how to improve the product, you can:
+We welcome community contributions to Intel(R) oneAPI Data Analytics Library. You can:
 
-* Let us know about your proposal via [Issues on oneDAL GitHub\*](https://github.com/oneapi-src/oneDAL/issues).
-* Contribute your changes directly to the repository through [pull request](#pull-requests). 
+- Submit your changes directly with a [pull request](https://github.com/oneapi-src/oneDAL/pulls).
+- Log a bug or make a feature request with an [issue](https://github.com/oneapi-src/oneDAL/issues).
+
+Refer to our guidelines on [pull requests](#pull-requests) and [issues](#issues) before you proceed.
+
+## Issues
+
+Use [GitHub issues](https://github.com/oneapi-src/oneDAL/issues) to:
+- report an issue
+- make a feature request
+
+**Note**: To report a vulnerability, refer to [Intel vulnerability reporting policy](https://www.intel.com/content/www/us/en/security-center/default.html).
 
 ## Pull Requests
 
 To contribute your changes directly to the repository, do the following:
 - Make sure you can build the product and run all the examples with your patch.
 - Make sure your code is in line with our [coding style](#code-style) as `clang-format` is one of the checks in our public CI.
 - For a larger feature, provide a relevant example.
+- [Document](#documentation-guidelines) your code.
 - [Submit](https://github.com/oneapi-src/oneDAL/pulls) a pull request into the `master` branch.
 
 Public and private CIs are enabled for the repository. Your PR should pass all of our checks. We will review your contribution and, if any additional fixes or modifications are necessary, we may give some feedback to guide you. When accepted, your pull request will be merged into our GitHub* repository.
@@ -49,6 +60,10 @@ Refer to [ClangFormat documentation](https://clang.llvm.org/docs/ClangFormat.htm
 
 For your convenience we also added [coding guidelines](http://oneapi-src.github.io/oneDAL/contribution/coding_guide.html) with examples and detailed descriptions of the coding style oneDAL follows. We encourage you to consult them when writing your code.
 
+## Documentation Guidelines
+
+oneDAL uses `Doxygen` for inline comments in public header files that are used to build the API reference and  `reStructuredText` for the Developer Guide. See [oneDAL documentation](https://oneapi-src.github.io/oneDAL/) for reference.
+
 ---
 **Note:** oneDAL is licensed under [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0). By contributing to the project, you agree to the license and copyright terms therein and release your contribution under these terms.