Update l2-transfer-tools-guide.mdx (#468)

Added link to the youtube video tutorial going over transferring a subgraph

Author: marcusrein

website/pages/en/arbitrum/l2-transfer-tools-guide.mdx

@@ -10,6 +10,8 @@ Some frequent questions about these tools are answered in the [L2 Transfer Tools
 
 ## How to transfer your subgraph to Arbitrum (L2)
 
+Watch a [video walkthrough](https://youtu.be/R8_vz4lx2Co) of this process.
+
 ## Benefits of transferring your subgraphs
 
 The Graph's community and core devs have [been preparing](https://forum.thegraph.com/t/gip-0031-arbitrum-grt-bridge/3305) to move to Arbitrum over the past year. Arbitrum, a layer 2 or "L2" blockchain, inherits the security from Ethereum but provides drastically lower gas fees.