Add description and CLI arguments to graph plugin README
</p>
<br/>
-Description goes here
+The FASTEN Graph Plugin is a tool for inserting [GID Graphs](https://github.com/fasten-project/fasten/wiki/GID-Graph-format) into Graph database ([RocksDB](https://rocksdb.org/)) and retrieveing them from it. The graph plugin can be used as a standalone tool and as a part of FASTEN server.
## Arguments
-CLI arguments go here
+- `-h` `--help` Show this help message and exit.
+- `-f` `--file` Path to JSON file which contains GID Graph
+- `-d` `--dir` The directory of the RocksDB instance
## Usage
-#### Some example
+#### Insert GID Graph in the database
```shell script
-man example
+ -f gid_graphs/graph.json -d data/graphdb
```
