Adjust transferability texts when the stream is non-transferable

[PaulRBerg]

Problem

Owners of non-transferable streams are confused about the current NFT-related texts. Specifically, the description that makes part of the token URI.

Solution

Adjust the text when the stream NFT is non-transferable. I.e. instead of this:

⚠️ WARNING: Transferring the NFT makes the new owner the recipient of the stream. The funds are not automatically withdrawn for the previous recipient.

Say something like this (final text to be decided during PR review):

NOTE: This is a non-transferable NFT. It is possible to list it on NFT marketplaces but the final sale cannot be performed.

Context

See this listing on OpenSea: https://opensea.io/assets/ethereum/0xafb979d9afad1ad27c5eff4e27226e3ab9e5dcc9/3408