Improve README for developers without OBS experience

[thigg]

From the Readme:

Make your software package successfully compile at the Sailfish OS OBS.

If you never worked with OBS it would be helpful to get some pointers on how to complete this step. Maybe there is some documentation that could be linked or maybe a few apps as examples (c with dependencies, python+QML,QML only, QML+webview+some webapp that needs to be built)

[Thaodan]

Most documentation on this can be taken from the official wiki and if something is missing on that should be extended there.
https://docs.sailfishos.org/Tools/Sailfish_SDK/Building_packages/#building-packages-remotely

[Dracks]

One question, the OBS of sailfish.org is not dead?

https://build.sailfishos.org/

[rinigus]

No, we have https://build.merproject.org working

[Olf0]

A PR resolving this issue is welcome. IMO it should (at least) contain aforementioned web-link to Jolla's documentation, plus denoting that the DNS domain merproject.org currently must be used for all SailfishOS-OBS related web-links.

[Olf0]

https://build.sailfishos.org/ has been working well again for more than a year now.

https://build.merproject.org/ is now redirected to https://build.sailfishos.org/, fortunately retaining a subsequent, specific URL.