README.org: Change `symbol' to =symbol= so org styles it.

This was done using `query-replace-regexp' "`\(\(?:\s_\|\w\)+\)'" => "=\1=".
README.org: Make image links relative.
README.org: Fix up grammar.
Add timer to delay popup
Update docs to describe idle-delay
Merge pull request #3 from haxney/readme-fixes

Readme fixes
Merge pull request #5 from deprecated/idle-delay