fix(docs): Correct typo and grammar in CONTRIBUTING.md (#252)

Author: AbdulRehman-Fayyaz

CONTRIBUTING.md

@@ -6,7 +6,7 @@ We appreciate all kinds of contributions to this project. This document gives yo
 
 - We suggest to follow the common workflow based on issues and pull requests. In the issue, you should describe the problem. Based on this discussion, one can create a pull request that should solve the issue.
 - A good issue describes what is wrong and why it is wrong. Ideally, one has already a suggestion on how to fix the problem, but the suggestions is not mandatory.
-- A good pull request should refer to the issue and thus to the problem that it should solve. Explain what the pull request does and how it addresses the problem/issue. If you still work on a new feature or a fix, you can open a pull request and mark is as draft. Once you consider the work done, please mark it as ready for review and request a reviewer. We will give feedback and eventually merge the pull request.
+- A good pull request should refer to the issue and thus to the problem that it should solve. Explain what the pull request does and how it addresses the problem/issue. If you are still working on a new feature or a fix, you can open a pull request and mark it as draft. Once you consider the work done, please mark it as ready for review and request a reviewer. We will give feedback and eventually merge the pull request.
 - We enforce consistency of the formatting via automatic style checking. When marking a pull request as ready for review, please make sure that all checks pass successfully.
 - For *small changes*, such as typos, broken links etc., please directly create a pull request.
 - For larger changes, such as the description of new tools, a new chapter etc., please open an issue first.