Update the documentations with the latest requirements and restore the transifex link

[NyanKiyoshi]

Python 3.4 was dropped in #2601, this change replace the minimal Python version 3.4 to 3.5 in the documentations.

This also the restore the transifex link that was accidentally removed from the readme file.

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. The changes are tested.
6. The code is documented (docstrings, project documentation).

[Pacu2]

Wonder if translate should be on its own, or under Contribute section?

[patrys]

It should probably also say Node.js 10+

[Pacu2]

Also, Python and Node versions get listed in other places, like installation docs for linux

[Pacu2]

I'm also missing some invitation to contribute in the copy.
Maybe something like

Did you know that Saleor is available in almost 30 languages, translated entirely by our community? 
If you'd like to help us, you can join one of our translation teams on [the localization platform Transifex](https://www.transifex.com/mirumee/saleor-1/languages/).
The repository gets synchronized weekly with the latest contributions.

[Pacu2]

It's hard to say which emoji this is, I think that earth emoji 🌎 would be more readable

https://emojipedia.org/earth-globe-europe-africa/

[NyanKiyoshi]

America 🌎 or Europe-Africa 🌍?

[Pacu2]

America is better-looking, but that's the matter of preferences 😏

[NyanKiyoshi]

Less details shown 👍

[NyanKiyoshi]

@Pacu2 we could put it under the contribute section, but it would probably be too much in a single section. We could split it up to two sub sections, but would not be looking better (by far).

I think it would be better to keep it separated for the visual and to quickly catch the localization section. But maybe it would be better to move it below the Contribute section. What do you think?

[codecov]

Codecov Report

Merging #2656 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2656   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files         204      204           
  Lines        9898     9898           
  Branches      932      932           
=======================================
  Hits         8868     8868           
  Misses        746      746           
  Partials      284      284

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