Improve and cleanup the PR template

[Lexedia]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Use smart commits here to manipulate issues (eg. Fixes #issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• Ran dart analyze .
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works