Add a What are plugins section

I think it could be important. I found it a bit complicated writing a decent description, but I think it sums it up.
Removed newline at end of file.
Added a bit of matter.
Merge pull request #27 from CoWinkKeyDinkInc/master

Get rid of blockquote looking text.
Merge pull request #28 from dannyps/patch-1

Add to Installing Plugins page
Cleaned up text a bit (by any dev is implied).
Merge pull request #1 from SpongePowered/master

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