Merge #213

213: add comment on where to look to view 'Hello World' message r=jrvanwhy a=JOE1994

This PR adds a one helping comment to the example program **examples/hello_world.rs**.
The comment tells where to look to see the "Hello World" message printed out.

I thought adding this line would be helpful to newcomers like me :smile_cat: 

p.s. 
Is running `tockloader listen` the canonical way to view messages printed to the console?

Thank you for reviewing this PR :) :cake: 

Co-authored-by: JOE1994 <joseph942010@gmail.com>

examples/hello_world.rs

diff --git a/examples/hello_world.rs b/examples/hello_world.rs
index 4a67404..052cf69 100644
--- a/examples/hello_world.rs
+++ b/examples/hello_world.rs
@@ -1,4 +1,6 @@
 // This example just prints "Hello Tock World" to the terminal.
+// Run `tockloader listen`, or use any serial program of your choice
+//  (e.g. `screen`, `minicom`) to view the message.
 
 #![no_std]