Remove long snippet and add description

Author: tapaswenipathak

docs/source/command_line.rst

@@ -452,19 +452,10 @@ in error messages.
 ``--no-color-output``
     This flag will disable color output in error messages, enabled by default.
 
-``--error-summary``
-    This flag will show error messages with stats summary,
-    for example, the following indicates an error summary::
-        from typing import List
-        x = []  # type: List[float]
-        y = []  # type: List[int]
-        x = y
-        bad.py:4: error: Incompatible types in assignment (expression has type
-        "List[int]", variable has type "List[float]")
-        bad.py:4: note: "List" is invariant -- see
-        http://mypy.readthedocs.io/en/latest/common_issues.html#variance
-        bad.py:4: note: Consider using "Sequence" instead, which is covariant
-        Found 1 error in 1 file (checked 1 source file)
+``--no-error-summary``
+    This flag will show error messages with stats summary, enabled by default.
+    By default mypy shows a summary line including total number of errors,
+    number of files with errors, and number of files checked.
 
 .. _incremental: