DOC: Add warning for newbs not to edit auto-generated file

Author: Garrett-R

pandas/src/generate_code.py

@@ -1,3 +1,10 @@
+"""This file generates `generated.pyx` which is then included in `../algos.pyx`
+during building.  To regenerate `generated.pyx`, just run:
+
+    `python2 generate_code.py`.
+
+"""
+
 from __future__ import print_function
 # we only need to be able to run this file on 2.7
 # don't introduce a pandas/pandas.compat import
@@ -7,6 +14,12 @@
 
 _int64_max = np.iinfo(np.int64).max
 
+warning_to_new_contributors = """
+# DO NOT EDIT THIS FILE: This file was autogenerated from generate_code.py, so
+# please edit that file and then run `python2 generate_code.py` to re-generate
+# this file.
+"""
+
 header = """
 cimport numpy as np
 cimport cython
@@ -2528,6 +2541,7 @@ def generate_from_template(template, exclude=None):
 
 def generate_take_cython_file(path='generated.pyx'):
     with open(path, 'w') as f:
+        print(warning_to_new_contributors, file=f)
         print(header, file=f)
 
         print(generate_ensure_dtypes(), file=f)

pandas/src/generated.pyx

@@ -1,4 +1,9 @@
 
+# DO NOT EDIT THIS FILE: This file was autogenerated from generate_code.py, so
+# please edit that file and then run `python2 generate_code.py` to re-generate
+# this file.
+
+
 cimport numpy as np
 cimport cython