Update 'echo -n' example

Putting `echo -n` in backticks isn't a productive example, since command
substitution (backticks, or `$()` in Bash) already removes the trailing
newline(s).

References:
* <https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html>
* <http://heirloom.sourceforge.net/sh/sh.1.html#4>

README.md

@@ -2590,7 +2590,9 @@ printf 'hello world\n%.0s' {1..5}
 ```
 ##### Do not echo the trailing newline
 ```bash
-username=`echo -n "bashoneliner"`
+echo -n "Doing the things... "
+# (do things)
+echo "done."
 ```
 
 ##### Copy a file to multiple files (e.g copy fileA to file(B-D))