Reorder and update installation instructions

[fso42]

CURRENTLY PR is here for the online check of the documentation
https://docs.avaframe.org/en/docfor1.3/

• In preparation for automatic installation via the connector

[codecov]

Codecov Report

Base: 74.80% // Head: 74.80% // No change to project coverage 👍

Coverage data is based on head (22ac445) compared to base (6f2fd21).
Patch has no changes to coverable lines.

❗ Current head 22ac445 differs from pull request most recent head 7f5a355. Consider uploading reports for the commit 7f5a355 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #774   +/-   ##
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  Coverage   74.80%   74.80%           
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  Files          57       57           
  Lines       12033    12033           
=======================================
  Hits         9001     9001           
  Misses       3032     3032           

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[awirb]

• In the manuelle Installation Note the error is not the same style as the one in the english version, maybe :: missing?

• in the development installation, consider saying: Create a new conda environment for AvaFrame, activate it and install pip, NUMPY and CYTHON in this environment:

• in the Standard Installation, consider linking the AvaFrameConnector to its page so that there is a direct link, or that it is clear that there is another page where more info is provided?

[qlty-cloud-legacy]

Code Climate has analyzed commit d0adfbd and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 72.7% (0.0% change).

View more on Code Climate.