doc: add description and topics of this repo

[wey-gu]

Desc:

• Nebula-Algorithm is a Spark Application based on GraphX, which enables state of art Graph Algorithms to run on top of NebulaGraph and write back results to NebulaGraph.

Topics:

• Graph-Database
• Graph-Algorithm
• Spark
• GraphX
• NebulaGraph

Please @Nicole00 help rephrase and when it's OK, please @Shinji-IkariG help edit on the repo :)

Thanks

[Nicole00]

Thanks for your thoughtful consideration. how about write back results to NebulaGraph?

[wey-gu]

Thanks for your thoughtful consideration. how about write back results to NebulaGraph?

Done :)

[wey-gu]

@Shinji-IkariG could you please help update the repo? thanks

[Shinji-IkariG]

All Done