Better doc for the -c command.

Author: erezsh

README.md

@@ -195,7 +195,9 @@ Options:
   - `--help` - Show help message and exit.
   - `-k` or `--key-column` - Name of the primary key column
   - `-t` or `--update-column` - Name of updated_at/last_updated column
-  - `-c` or `--columns` - Name or pattern of extra columns to compare. Pattern syntax is like SQL, e.g. `%foob.r%`.
+  - `-c` or `--columns` - Names of extra columns to compare.  Can be used more than once in the same command.
+                          Accepts a name or a pattern like in SQL.
+                          Example: `-c col% -c another_col -c %foorb.r%`
   - `-l` or `--limit` - Maximum number of differences to find (limits maximum bandwidth and runtime)
   - `-s` or `--stats` - Print stats instead of a detailed diff
   - `-d` or `--debug` - Print debug info

data_diff/__main__.py

@@ -52,7 +52,15 @@ def _get_schema(pair):
 @click.argument("table2", required=False)
 @click.option("-k", "--key-column", default=None, help="Name of primary key column. Default='id'.")
 @click.option("-t", "--update-column", default=None, help="Name of updated_at/last_updated column")
-@click.option("-c", "--columns", default=[], multiple=True, help="Names of extra columns to compare")
+@click.option(
+    "-c",
+    "--columns",
+    default=[],
+    multiple=True,
+    help="Names of extra columns to compare."
+    "Can be used more than once in the same command. "
+    "Accepts a name or a pattern like in SQL. Example: -c col% -c another_col",
+)
 @click.option("-l", "--limit", default=None, help="Maximum number of differences to find")
 @click.option("--bisection-factor", default=None, help=f"Segments per iteration. Default={DEFAULT_BISECTION_FACTOR}.")
 @click.option(