feat: explain light weight even more

[sesam]

under scalable header on the site we should mention that due to the default pruning a full node is nearly as light as an SPV client so even very weak hardware can connect to the network, adding to our premise of usability by anyone even with limited access

cc @0xb100d

[0xb100d]

Something to the effect that the unique nature of mimblewimble format allows all txs to be validated with a minimial amount of data, and onging research will likely allow more and more complete validation to be done with smaller and smaller amounts of space and processing overheads to the point where even mobile light clients will have almost all the same security assumptions as a full client, and contribute to the security of the network.