Add Tolk syntax highlighting to GitHub

[Vladimir-Khm]

Tolk 1.0 makes a significant step in TON smart contract development. To solidify its position and visibility, GitHub syntax highlighting is essential. It not only enhances usability but also establishes Tolk as a recognized ecosystem language

Since Tact already has GitHub highlighting, providing the same for Tolk reinforces its importance within the ecosystem

[tolk-vm]

We'll do this as soon as there are many *.tolk files created on GitHub (across all repositories, by a global search).
There are some limits GitHub has, and hopefully, we'll overcome them quite soon.

[SonnyPlayer]