Add Galician patterns

[deivisCode]

I have 0 rust experience, so just in case, this is exactly what I did:

• I first added the patterns from https://github.com/hyphenation/tex-hyphen/blob/master/hyph-utf8/tex/generic/hyph-utf8/patterns/tex/hyph-gl.tex
• Then edited the Cargo.toml, and tests/generate (following the changes made for Catalan language)
• Run cargo test --tests generate two times, first failed, second succeded
• src/lang.rs gets correctly updated
• Edited README accordingly