Add License file (LGPL)

License is LGPL 2 confirmed via:
 * License specified in: https://sourceforge.net/projects/dacco/
 * Mail from Linda Oxnard to the DACCO contributors (Date: Thu, 8 Oct 2020 10:40:31 -0400, Subject: Re: Dacco revival?)
 * FOSDEM talk: https://www.slideshare.net/cpina/dacco (slide 12)

The original CVS repository didn't specify a license for the repository besides in the file: `input/engcat/catSpeakerPublish.xsl`