add nft bridge examples and marketplace integration doc

[souradeep-das]

• adds a NFT bridge to L1 example and tutorial
• adds guide and example scripts for marketplace bridge integration

[codecov-commenter]

Codecov Report

Merging #470 (d3e2d54) into develop (14cefb2) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #470   +/-   ##
========================================
  Coverage    72.10%   72.10%           
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  Files           59       59           
  Lines         1828     1828           
  Branches       281      281           
========================================
  Hits          1318     1318           
  Misses         510      510           

Flag	Coverage Δ
contracts	86.72% <ø> (ø)
core-utils	53.79% <ø> (ø)
data-transport-layer	29.25% <ø> (ø)
message-relayer	83.17% <ø> (ø)

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[boyuan-chen]

Can we remove the build folder? Also, we need to mention that developers have to contact us to add the pairs in the NFT bridges. It will be nice if we can add the script to allow them to directly test on Rinkeby, so they don't have to spend a day figuring out how to spin up the local stack. The fraud proof window of Rinkeby is 5 mins, so they can exit their NFT from L2 quickly.

[CAPtheorem]

Can we remove the build folder? Also, we need to mention that developers have to contact us to add the pairs in the NFT bridges. It will be nice if we can add the script to allow them to directly test on Rinkeby, so they don't have to spend a day to figure out how to spin up the local stack. The fraud proof window of Rinkeby is 5 mins, so they can exit their NFT from L2 quickly.

Yes, @souradeep-das please add that

[souradeep-das]

sure, reiterating the pair registration part, yeah the only reason the dependency on local stack is to have the essence of using your own contracts (because of the registration part), but nice idea, will add an optional quickstart on rinkeby for people, which can work with pre-deployed preset contracts

[CAPtheorem]

moved to /bobanetwork