[z2303] Add helper script to easily create a topic branch

(based on commit [12422] - 9245f5f)

Signed-off-by: DasBlub <DasBlub@gmail.com>
[z2304] Add a helper script to easily merge topic branches and pull-requests

(based on commit [12423] - 0136df7)

Signed-off-by: DasBlub <DasBlub@gmail.com>
[z2305] Add Contributing Guidelines

[ci skip]

(based on commit [12424] - e329b31)

Signed-off-by: DasBlub <DasBlub@gmail.com>