Fix typo

.github/CONTRIBUTING.md

@@ -9,17 +9,16 @@ BEGINRELEASENOTES/ENDRELEASENOTES block, which will appear in the
 doc/ReleaseNotes.md, once a new tag is made.
 
 We are happy if you create pull-requests also if you feature is not ready, yet.
-Please mar them as such by adding `[WIP]` to the start of the title. The purpose
+Please mark them as such by adding `[WIP]` to the start of the title. The purpose
 of this is, for example, that you want to let other people know you are working
 on a given issue. For these work-in-progress pull-request, we propose to have a
 check list of things that still need to be done.
 
 ## Issue tracking
 
-Use the github issue tracker. Reference the issues that you are working on. If
-you notice an issue, consider first creating an issue and then refering to it in
-your pull-request and commit messages with `#[issue-id]`.
-
+Use the GitHub issue tracker. Reference the issues that you are working on.
+If you notice an issue, consider first creating an issue and then refering to it
+in your pull-request and commit messages with `#[issue-id]`.
 
 ## Coding Conventions