Improve Example of Working with Charts

[lovtsovaik]

Environment

• Documentation version: 7.2
• Part of the documentation: Charts
• Existing page: https://doc.cuba-platform.com/charts-7.2/charts.html#chart_example

Description of the bug or enhancement

§2.6.2

• There is no description of how to add a chart to the screen, as described, for example, in §2.6.3.2
• There is no description of how to see the result (Start application server and Log in)
  This confuses the reader who has opened the examples since this is the first example.

§2.6.3.2

• Typo in code: fillAlphas="09.", expected fillAlphas="0.9"

§2.6.3.2, §2.6.4.1
In RU documentation: delete .xml from the Descriptor name field