Update sky/sdk/README.md instructions

Update sky/sdk/README.md instructions

R=ianh@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/18027b7d1e9a8a40979879f757d22fcda1fb73a8

[Hixie, 2015-04-27 21:28:34]

lgtm

[eseidel, 2015-04-27 21:28:49]

Committed patchset #1 (id:1) manually as
18027b7d1e9a8a40979879f757d22fcda1fb73a8 (presubmit successful).

[Matt Perry, 2015-04-27 21:32:26]

mpcomplete@chromium.org changed reviewers:
+ mpcomplete@chromium.org

[Matt Perry, 2015-04-27 21:32:27]

https://codereview.chromium.org/1107203003/diff/1/sky/sdk/README.md
File sky/sdk/README.md (right):

https://codereview.chromium.org/1107203003/diff/1/sky/sdk/README.md#newcode136
sky/sdk/README.md:136: 1. ``packages/sky/lib/sky_tool --install
examples/stocks/main.sky``
This didn't work for me. I get this error:

> ./packages/sky/lib/sky_tool --install examples/stocks/main.sky                
 
usage: sky_tool [-h] {start,stop} ...
sky_tool: error: invalid choice: 'examples/stocks/main.sky' (choose from
'start', 'stop')

I get further (but I still hit errors) if I run this:

> ./packages/sky/lib/sky_tool start examples/stocks/main.sky
Serving HTTP on 0.0.0.0 port 9888 ...
Starting: Intent { act=android.intent.action.VIEW
dat=sky://localhost:9888/main.sky }
127.0.0.1 - - [27/Apr/2015 17:30:36] "GET /main.sky HTTP/1.1" 200 -
127.0.0.1 - - [27/Apr/2015 17:30:36] "GET /lib/stock_app.dart HTTP/1.1" 200 -
127.0.0.1 - - [27/Apr/2015 17:30:36] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:36] "GET
/packages/sky/framework/components/action_bar.dart HTTP/1.1" 404 -
127.0.0.1 - - [27/Apr/2015 17:30:36] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:36] "GET
/packages/sky/framework/components/drawer.dart HTTP/1.1" 404 -
127.0.0.1 - - [27/Apr/2015 17:30:37] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:37] "GET
/packages/sky/framework/components/drawer_header.dart HTTP/1.1" 404 -
127.0.0.1 - - [27/Apr/2015 17:30:37] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:37] "GET
/packages/sky/framework/components/floating_action_button.dart HTTP/1.1" 404 -
127.0.0.1 - - [27/Apr/2015 17:30:37] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:37] "GET
/packages/sky/framework/components/action_bar.dart HTTP/1.1" 404 -
127.0.0.1 - - [27/Apr/2015 17:30:37] code 404, message File not found
127.0.0.1 - - [27/Apr/2015 17:30:37] "GET
/packages/sky/framework/components/drawer.dart HTTP/1.1" 404 -

[eseidel, 2015-04-27 21:34:55]

Correct.  I'm about to fix that.  The problem is that my instructions assume
you're using the dart_summit branch of sky_sdk.  I'm going to delete the
dart_summit branch of sky_sdk and just make mainline be the correct one, despite
it having been created from a branch of mojo.