No ready for GF yet

[RosaWagner]

Hi @sursly ! @emmamarichal was having issues building this font due to the custom axis (cf https://github.com/google/fonts/issues/4625#issuecomment-1191455372). So I made a build system and once this PR is merged, she can continue to make the font ready for GF.

We have upgraded our documentation, and if you have issue using gftools builder, you can read these chapters:

• https://googlefonts.github.io/gf-guide/tools
• https://googlefonts.github.io/gf-guide/build.html#gftools-builder

[sursly]

Didn't know y'all were doing this. Awesome! Thanks @RosaWagner and @emmamarichal