Move Micro TVM top level page

[hogepodge]

The micro TVM page was moved during a recent docs update. This
patch moves the top level index to the former location.

[hogepodge]

@tqchen @areusch @merrymercy

[merrymercy]

I moved it to MISC because I think microTVM is similar to VTA, which is placed under MISC section.
microTVM does not fit into “How to” section very well.

[tqchen]

Given uTVM is an important domain that could warrant a different kinds of treatment. I think it is a good idea to keeping a landing page at the top-level(perhaps under a get started section). let us consider revert to the previous state and then think about new overall structure.

[areusch]

originally my intent with the microTVM page was to serve as an organizational landing page for topics relating to microTVM. I agree VTA has a similar structure. I don't think Misc is the right place for such pages, but I also agree that Getting Started doesn't entirely make sense either given the way we structure the rest of the repo. I do think we could use more top-level pages in the documentation site to help organize the documentation, but we can contemplate that in a broader PR/RFC.