Add brief importable default methods description.

libconsensus/__init__.py

@@ -3,5 +3,6 @@ __licence__ = "GNU GPLv3"
 __version__ = 0.1
 from .libconsensus import (
     ali2cons,
+    default_cons_methods,
     fasta2cons,
     )

libconsensus/libconsensus.py

@@ -106,6 +106,15 @@ def counts_add(cumul_counts, counter_item):
     return cumul_counts[1] + counter_item[1]
 
 
+# This should be updated if `col_consensus` changes.
+default_cons_methods = """
+A consensus of the aligned sequences was computed using a rather conservative approach:
+
+If one nucleotide accounted for at least 75% of an alignment column, this column was represented by this nucleotide.
+Otherwise, the "N" ambiguity code was used.
+"""
+
+
 def col_consensus(column, cum_freq=0.75, do_iupac=False):
     """
     Determine the consensus of the letters present in *column*.