[charts][docs] Revise the Radar doc

[mapache-salvaje]

• I have followed (at least) the PR section of the contributing guide.

[mui-bot]

Deploy preview: https://deploy-preview-21674--material-ui-x.netlify.app/

Updated pages:

• docs/data/charts/radar/radar.md

Bundle size report

Bundle	Parsed size	Gzip size
@mui/x-data-grid	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
@mui/x-charts	0B(0.00%)	0B(0.00%)
@mui/x-charts-pro	0B(0.00%)	0B(0.00%)
@mui/x-charts-premium	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers-pro	0B(0.00%)	0B(0.00%)
@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

Generated by 🚫 dangerJS against c36bc0f

[codspeed-hq]

Merging this PR will not alter performance

✅ 14 untouched benchmarks

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_{Comparing mapache-salvaje:feature/dx-145-revise-the-charts-radar-doc (56c8d3d) with master (71ec303)¹}

Footnotes

1. No successful run was found on master (ca328ad) during the generation of this report, so 71ec303 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩