Ah, seems I misunderstood the question since a segwit implementation is already in bitcoin core.
Geez but is not really fleshed out so you have to do everything manually.
I believe full segwit support will come in the next update.
May I ask one question? If I create a Segwit wallet on Electrum, can I use that wallet to send/receive bitcoins from Legacy wallets? Also, will I be able to use the Lightning Network?
Segwit addresses and transactions are backwards compatible with legacy addresses (except in the case of "native segwit" addresses AKA Bech32 -- the ones that start with bc1)
Bech32 addresses are not backwards compatible with legacy software so you'll have to update your wallet to be able to SEND funds to such addresses of your wallet is not updated, but you can always RECEIVE funds from them.
Yes, you'll be able to use the lightning network with Segwit addresses.
IIRC you can only use the lightning network with Segwit addresses because they're the only ones with the transaction malleability fix which makes lightning work seamlessly.