wiki: suggestion and typo

The Diagnostics section should mention lintr, e.g.:

The language server provides code diagnostics through the [lintr](https://lintr.r-lib.org/) package in R. See [here](https://github.com/REditorSupport/vscode-R/wiki/Code-linting) for configuration.

and in the table of content:

-[Diagnose potential errors and unreliable code](https://github.com/REditorSupport/vscode-R/wiki/R-Language-Service#diagnostics)
+[Diagnose with `lintr` potential errors and unreliable code](https://github.com/REditorSupport/vscode-R/wiki/R-Language-Service#diagnostics)

(same wording as for the reference to styler in the Formatting section and table of content)

There is a typo in the Formatting section:

-The language server provides code formatting through the through the [styler](https://github.com/r-lib/styler) package in R. See [here](https://github.com/REditorSupport/languageserver#customizing-formatting-style) for configuration.
+The language server provides code formatting through the [styler](https://github.com/r-lib/styler) package in R. See [here](https://github.com/REditorSupport/languageserver#customizing-formatting-style) for configuration.

Open the R-Language-Service wiki page and review its Diagnostics and Formatting sections plus the table of contents. Add the lintr description and link, update the diagnostics wording, and remove the duplicated “through the” in the styler sentence. Done means both wiki sections and their table-of-contents entries match the wording requested.