servo: Merge #10914 - Added documents for commandline arguments (from shinglyu:docs); r=aneeshusa

An initial draft for #10878

Source-Repo: https://github.com/servo/servo
Source-Revision: 3f2ceeff5dd1966dafe34381e20ec405ab72ccee

servo/docs/COMMAND_LINE_ARGS.md

@@ -0,0 +1,32 @@
+Command Line Arguments
+========================
+# General
+
+You can see available commands with:
+```
+./mach -h
+./mach <sub-command> -h
+```
+Only arguments that need more explanation will be documented here.
+
+# Run
+## Enable Experimental Features
+Use `--pref` to enable experimental features like experimental DOM API, JavaScript API and CSS properties.
+
+e.g. To enable `flex` and `flex-direction` css properties:
+```
+./mach run -d -- --pref layout.flex.enabled --pref layout.flex-direction.enabled ...
+```
+
+You can find all the available preferences at [resources/prefs.json](http://mxr.mozilla.org/servo/source/resources/prefs.json).
+
+# Debugging
+## Remote Debugging
+Use `--devtools 6000` to start the devtools server on port 6000.
+
+e.g.
+```
+./mach run -d --devtools 6000 https://servo.org
+```
+
+To connect to the server, follow [this guide](https://developer.mozilla.org/en-US/docs/Tools/Remote_Debugging/Debugging_Firefox_Desktop#Connect).