I split this into a separate discussion. Indeed it looks like Stack Exchange and Community flavors of markdown do not support tables yet:

Is there any markdown to create tables?

We will look into it. It would be good to have especially with tools like THIS. Perhaps a solution could be placing WL generated TeX output between $$ tags. For example:

TeXForm[
 TableForm[
  {{A, B},
   {C, D}}
  ]
 ]

\begin{array}{cc}
 A & B \\
 C & D \\
\end{array}

so it should look like a table but it does not - though it does in preview:

$$ \begin{array}{cc} A & B \ C & D \ \end{array} $$

And I agree - GitHub syntax integration would be nice. Any further ideas are welcome.

Do you mean a table similar to your GitHub page? Would simply copying table syntax from GitHub page here work? GitHub, Community and Stack Exchange all use the same so called markdown syntax, but they have different flavors of it. So I am not sure if table will work but maybe it is worth a shot.