Update language descriptions and links

[novusnota]

Why is it important?

• Added a link to Tact docs from the sidebar
• Updated the description of Tact language (both English and Chinese)
• Unified sidebar and navbar link order, from the most high-level (such as Tact and Tolk) to the most low-level (such as Fift and TL-B). That makes all languages easies to discover and visually conveys the idea of "digging deep" and learning more.

Preview

[novusnota]

Simplified and shrank the description to better match the rest of the page:

[novusnota]

...And now edited to be more formal and clear:

[novusnota]

@reveloper If the order from higher to lower-level languages doesn't feel right to you, we can inverse it and go from lower (TL-B and Fift) to higher (Tolk and Tact). But I assumed that placing more accessible languages first (Tact and Tolk) would be more beneficial to users, hence this sorting.

That said, the current order is just a seemingly random shuffle:

[reveloper]

@novusnota your language order seems more convenient according to the developer community position.
Thank you!