doc: Update Linux installation instructions.
doc: Update Linux installation instructions.

- g++ is needed for Linux
- X11 headers are optionally needed for Linux

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apitrace/apitrace,trtt/apitrace,schulmar/apitrace,EoD/apitrace,trtt/apitrace,schulmar/apitrace,EoD/apitrace,trtt/apitrace,trtt/apitrace,apitrace/apitrace,trtt/apitrace,apitrace/apitrace,apitrace/apitrace,EoD/apitrace,schulmar/apitrace,schulmar/apitrace,EoD/apitrace,EoD/apitrace,schulmar/apitrace