Update docs about local files support for "scrapy shell"

docs/topics/commands.rst

@@ -373,7 +373,9 @@ shell
 * Requires project: *no*
 
 Starts the Scrapy shell for the given URL (if given) or empty if no URL is
-given. See :ref:`topics-shell` for more info.
+given. Also supports UNIX-style local file paths, either relative with
+``./`` or ``../`` prefixes or absolute file paths.
+See :ref:`topics-shell` for more info.
 
 Usage example::
 

docs/topics/shell.rst

@@ -53,6 +53,36 @@ this::
 
 Where the ``<url>`` is the URL you want to scrape.
 
+:command:`shell` also works for local files. This can be handy if you want
+to play around with a local copy of a web page. :command:`shell` understands
+the following syntaxes for local files::
+
+    # UNIX-style
+    scrapy shell ./path/to/file.html
+    scrapy shell ../other/path/to/file.html
+    scrapy shell /absolute/path/to/file.html
+
+    # File URI
+    scrapy shell file:///absolute/path/to/file.html
+
+.. warning:: :command:`shell` will interpret ``index.html`` as a domain name,
+   not as a relative path to a local file, and will trigger a DNS lookup error::
+
+    $ scrapy shell index.html
+    [ ... scrapy shell starts ... ]
+    2016-01-26 10:29:51 [scrapy] DEBUG: Gave up retrying <GET http://index.html>
+    (failed 3 times): DNS lookup failed:
+    address 'index.html' not found: [Errno -5] No address associated with hostname.
+    [ ... traceback ... ]
+    twisted.internet.error.DNSLookupError: DNS lookup failed:
+    address 'index.html' not found: [Errno -5] No address associated with hostname.
+
+   Use ``./`` prefix instead::
+
+    $ scrapy shell ./index.html
+    [ ... scrapy shell starts ... ]
+
+
 Using the shell
 ===============