。
Distribution is permitted in accordance with the GPL rules.
Literal
GPL [possessive-の] rules [in accordance with-に従い], distribution-possible is.
A formal license notice. The ~可能 suffix attaches to nouns to make 'X is possible' — here 頒布 + 可能 = 'distribution is possible/permitted'. に従い is the literary/formal conjunctive form of に従って ('in accordance with'), preferred in written Japanese for its terser feel. 頒布 (はんぷ) is a formal term for distribution, specifically of documents, samples, or licensed material.