Update selecting-elements.md

[SoldierKB]

To :checked selector description added as well.

[eddiemonge]

that select looks weird by itself. I propose either pluralizing it or adding "elements" to it.

Also, @SoldierKB Could you please sign our CLA and update your git config to include your real name?

[SoldierKB]

As you wish - as far as english is not my native language I can not guarantee if my sentence is correct. You should modify it the way you think is correct.
In my profile on Github it is stated that my name is Bohdan Mel'nyk, and nick-name SoldierKB - not sure at all if I can change nick without account recreation.
CLA signed.

[SoldierKB]

Changed.