Recommended edits to Walkthrough.md file

[Osa-code]

A few edits for improved readability and to correct a few typos (new wording in highlighted in bold below)

a visual representation of how much of the channel balance can be sent vs received**. Please see the table and section Channel Balance Mode below for additional information**

Optimize for Receiving: For merchants who primarily receive inbound Lightning payments, the channels with high local balances (CAN RECEIVE column) will be shaded red. The goal is to keep your local balances as low as possible and remote balance as high as possible, so that you can receive more funds inbound.

Optimize for Sending: For exchanges, fiat gateways, and other operators who primarily send outgoing Lightning payments (CAN SEND), the channels with low local balances will be shaded red. The goal is to keep your local balances as high as possible, so that you can send more funds outbound.