Add model card: what this is, and which variants are valid

consolidate: drop the duplicated root copy

merged checkpoint ({'pair_id': 'polypythia-14m-s1s2', 'parent_a': 'EleutherAI/pythia-14m-seed1', 'parent_b': 'EleutherAI/pythia-14m-seed2', 'ceiling': '(floor-relative)', 'operator': 'average', 'alignment': 'naive', 'align_method': 'permutation', 'regime': 'indep_seed', 'eval_langs': 'eng', 'nll_merge': 28.1802, 'nll_floor': 5.1597, 'param_coverage': 1.0, 'MS': None})