aviary: Update --build help message. (#222)

aviary/aviary.py

@@ -260,11 +260,13 @@ def main():
 
     base_group.add_argument(
         '--build',
-        help='Build conda environments and then exits. Equivalent to \"--snakemake-cmds \'--conda-create-envs-only True \' \"',
+        help='Build conda environments necessary to run the pipeline, and then exit. Equivalent to "--snakemake-cmds \'--conda-create-envs-only True \' ". Other inputs should be specified as if running normally so that the right set of conda environments is built.',
         type=str2bool,
         nargs='?',
         const=True,
         dest='build',
+        metavar='yes|no',
+        default='no',
     )
 
     base_group.add_argument(