[Ecosystem > TON Connect > Integrate a dApp] Make use of AppKit over lower-level TON Connect SDKs

[novusnota]

Related to #245.

[novusnota]

Since AppKit got moved one level higher, the current guide is no longer related to it and instead is concerned with lower-level TON Connect libraries. That is, no changes are needed apart from, perhaps, adding a callout on top leading to AppKit documentation pages. Something along the lines of "use modern, higher-level alternative — AppKit".