Rename 'License.txt'

Use the standard file name.

Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>
Add 'requirements.txt' file

Add file and update README to suit.

Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>
Merge pull request #1 from stephenfin/feat/requirements-doc

Add 'requirements.txt' file