update contribution guidelines, remove redundant files (paritytech#1181)

* update contribution guidelines, remove redundant files

* removing doc ref labels, updating links on contribution

* add manifest formatting

* update title

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* update links to the new repo

* terminal friendly convention

* update doc guideline format

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Co-authored-by: Alexander Samusev <41779041+alvicsam@users.noreply.github.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>