New GF Guide index with rearranged texts and sections

[vv-monsalve]

This PR includes a layout of the content in sections based on the process that an average new user should normally follow to publish their fonts on GF:

1. Getting familiar with the basic needed bits -> Introduction
2. Creating/organizing the files on the GH repo, to begin with the process -> Upstream Repo
3. Mastering the font files to meet the spec -> Preproduction
4. Details on the production requirements and tools needed for it -> Production
5. Publishing the fonts, more oriented for experienced and team members -> Onboarding

The formating also includes:

• Single text line to give context for each section contents
• Bold emphasis for Starting Point + Must read contents
• Ordering from most important (starting and must) to less crucial contents (learn, template, them members)
• Some HTML tags that hopefully will add color to the labels as a visual aid to required bits.

On GitHub they still look like normal tags but they would look different once in HTML pages

Expected result would be:

[RosaWagner]

That is looking good!! I have few points to suggest for the layout, maybe let's discuss that today. But let's merge in the meanwhile ;)