Add dataset license information (odc-by)
#3709
by SAD1CXZC12DXZ - opened
Append the License section to the dataset README. The dataset reuses the odc-by license of its direct data source (HuggingFaceTB/smollm-corpus, python-edu subset), which is the most permissive license across its data sources and the DeepSeek-V2.5 synthesis model license.