Update openeew.com to make it better for new users and more consistent with the dashboard

[krook]

This issue can track the feedback in #docs from Grzegorz Kieszkowski:

Hi,
I have just found out this project and I was on the website for the first time ever 15 mins ago so I will just leave my input as it may be fresh:

What I was looking on website:

• overview of project
• goal of project
• current state of project
• tech stack
• community information (ex. info on communication tools, town hall meetings, contact information)
• blog post
• demo
• roadmap

In short: I was looking for answer to questions "what" and "why"
What got me confused:

• detailed information on how to build a sensor, install, create dashboard etc.
• detailed instructions
• in general: sections "sensors","detection","monitor","alarms","data"

In short: "how-to" was a bit overwhelming and page navigation was problematic
I think that detailed instructions should be kept in github repo. keeping instructions on website:

1. documentation will be outdated very fast
2. it will be hard to maintain
3. it reaches user much slower
4. it may be overwhelming for newcomers

However I feel that there should be clear and easy information with provided github links for buildin, installing, deploying, using product.

I would start with listing audience of OpenEEW. Two basic groups:

1. Users: Seeking for information on product usage. Probably none to junior technical skills and knowledge. They require clear and detailed instructions which will not overwhelm them. In other words, product without well designed documentation will not be successful as they simply will not be able to use it.

2. Contributors: Seeking for information on community, contribution, meetings, OpenEEW management, tech stack. Junior to advanced technical skills and knowledge.
   Common matters for both groups: project overview, introduction, demo, contact information,