Updated the extension paths and the run command in the readme file

[ArtunSubasi]

I noticed that the descirbed build-server command was not working because the example repositories were moved in GitHub. It works with the updated paths.

The run command wasn't working for me without the privileged flag. Therefore I added it to the run command example as it is described in https://github.com/fnproject/docs/blob/master/fn/operate/options.md

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