two years blog post (2019-06-23)

Add structure, write introduction, add more quotes to start page (having only one quote talking about 1 year of pmOS is a bit thin at this point in time).

Closes #105 (closed)

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I've recycled two images from the old start page in the introduction section. As always, feedback welcome, let me know if I forgot something in the headlines.

Preview as rendered by gitlab (lots of unsupported markup in there): https://gitlab.postmarketos.org/postmarketos/postmarketos.org/blob/2y-post/content/blog/2019-06-23-two-years.md

Latest screenshot: Screenshot_2019-06-23_postmarketOS_Two_years_of_postmarketOS