Document that "coding: utf-8" is supported in requirements.txt

Fixes pypa#7182

Author: ananyo2012

docs/html/reference/pip_install.rst

@@ -148,6 +148,8 @@ and the newline following it is effectively ignored.
 
 Comments are stripped *before* line continuations are processed.
 
+To interpret the requirements file in UTF-8 format add a comment ``# -*- coding: utf-8 -*-`` to the first or second line of the file.
+
 The following options are supported:
 
   *  :ref:`-i, --index-url <--index-url>`

news/7182.doc

@@ -0,0 +1 @@
+Document that "coding: utf-8" is supported in requirements.txt

src/pip/_internal/download.py

@@ -122,6 +122,9 @@ def get_file_content(url, comes_from=None, session=None):
 
     try:
         with open(url, 'rb') as f:
+            # Decode the encoding format
+            # Example: Following comment enables utf-8 format
+            # # -*- coding: utf-8 -*-
             content = auto_decode(f.read())
     except IOError as exc:
         raise InstallationError(