Correct typo and add doc for -p option

docs/userguide.rst

@@ -170,6 +170,8 @@ Here are all available options in **RPG**:
 
 **-o, -\\-outputfile**: Result file to output resulting peptides (default './peptides.xxx' depending of -\\-fmt).
 
+**-p, -\\-pka**: Define pKa values. Either 'ipc' or 'stryer' (default: ipc). IPC values come from `IPC_peptide <http://isoelectric.org/theory.html>`_ and Stryer values from Biochemistry Stryer, 7th edition.
+
 **-r, -\\-randomname**: Random (not used) output name file. See :ref:`random` for more information.
 
 **-q, -\\-quiet**: No standard output, only error(s).

rpg/RapidPeptidesGenerator.py

@@ -277,7 +277,7 @@ def main():
                         "overwritten.")
     parser.add_argument("-p", "--pka", metavar="", choices=['ipc', 'stryer'],
                         default="ipc", help="Define pKa values. Either 'ipc' "
-                        "or 'stryer (default: ipc)")
+                        "or 'stryer' (default: ipc)")
     group_output = parser.add_mutually_exclusive_group()
     group_output.add_argument("-o", "--outputfile", type=str, metavar="",
                               default="", help="Optional result file "

rpg/core.py

@@ -84,7 +84,7 @@ AA_PKA_IPC = {"Nterm" : 9.564,
               "R" : 12.503,
               "Y" : 10.071,
               "Cterm" : 2.383}
-"""pKa of important amino acid to compute pI (from IPC)."""
+"""pKa of important amino acid to compute pI (from IPC_peptide. See http://isoelectric.org/theory.html for details)."""
 
 def handle_errors(message="", err=1, error_type=""):
     """Custom handling of errors and warnings.