wiki: suggestion and typo

[ThomasSoeiro]

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.