add: CLI improvements and small documentation updates

Things done:
    * config path should search config file in the following order: cli
      option, environment, xdg_path
    * Implement a retrain command.
    * when you require more keys than the ones available in the input,
      stop the program.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/util.c b/src/util.c
index 4621836..9a00aa3 100644
--- a/src/util.c
+++ b/src/util.c
@@ -91,7 +91,7 @@ void usage(int exit_code)
 {
     FILE *fp = (!exit_code) ? stdout : stderr;
     fprintf(fp,
-            "Usage: ml train [Options] FILE\n"
+            "Usage: ml [re]train [Options] FILE\n"
             "   or: ml predict [-Ohv] [-f FORMAT] [-o FILE] [-p INT] FILE\n"
             "\n"
             "Options:\n"