Fix minor typos and file name in contributing docs (#1651)
# Description *Please include a summary of the changes and the related issue. Please also include relevant motivation and context, including:* - What does this PR do? This PR fixes two minor typos in the contributing top level docs, and fixes a broken link to another file. - Why are these changes needed? While reading the guidelines I noticed two small typos and a broken link to the documentation guidelines in the same directory. - How were these changes implemented and what do they affect? Both typos were fixed. The file has been renamed from `DOCUMENTATION_GUIDELINE.md` to `DOCUMENTATION_GUIDELINES.md` to match the link, as the link seems correct vs the filename. There are no other references to this file within this repo. There are no open issues related to this