Update AUTHORS.md

[signalwerk]

I added my name according to https://github.com/podofo/podofo/commit/7fb3abb108e5b0f75fb0397459e89e36facdca03

Not a big contribution. Please don't hesitate to decline if you think it's too less for being mentioned here.

• [x] Accept to license the library and tools code under the terms of the LGPL 2.0 or later
• [x] Accept to license the library and tools code under the terms of the MPL 2.0
• [x] Accept to license the test code under the terms of the MIT-0
• [x] Read contributions guidelines
• [x] Checked coding style
• [x] The commits sequence is clean without work in progress/bugged revisions and merge commits. In doubt, squash the commits and/or rebase master

[ceztko]

Did you author the Lua support?