Update README.md

[hydrian]

1. Cleaned up some grammar issues.
2. Also, I moved the sudo file from /etc/sudoers to /etc/sudoers.d/radeon-profile for better support over OS upgrades and to prevent conflicting issues.

[Oxalin]

Please complete modifications with the following ones in bold:
"Otherwise, the app needs to be run with root privileges to change the power profiles (and clocks readings sometimes). You can create a text file containing username ALL = NOPASSWD: /usr/bin/radeon-profile under /etc/sudoers.d/radeon-profile. Here is a tip to run the app as a normal user. Note that this involves changing permissions to system files: http://bit.ly/1dvQMhS"

[some-username-here1]

Since they haven't responded since, I've included changes from hydrian's fork into my own, followed by overlaying Oxalin's corrections on top of it, plus some other changes in the README.md too.
some-username-here1@35e435d

[Oxalin]

Since the development seems to have stalled, I applied it to my fork. Thank you.