Add "Release Notes/Known Bugs" to Changelog, update file format to markdown, standardize the format of previous entries

Per a request to have initial release notes that specifically listed known issues for this PE 3.2 release, and barred by time constraints from automating a pull from open issues in JIRA, this commit adds a Release Note and Known Bug section to the Changelog for the imminent 3.2 release. As it will display on the Forge, updates file type to markdown and standardizes previous entries.