add license and copyright headers

[andife]

When I tried to add a new distribution, the check of update_headers.py failed (I thought my header was correct).

• In my opinion it is not necessary to develop an own tool, because there is already a project for this: https://reuse.software/
• I removed the update_headers.py (I hope I have not overlooked any use) and introduced the reuse github action

To add a badge to README, the Project has to be registered at https://api.reuse.software/register

I used the following line to add copyright and license:
reuse annotate --copyright="Copyright Contributors to the Pyro project." --license="Apache-2.0" tutorial\source\sir_hmc.rst

With the changes in that PR I get the following:

(pyro_debug) C:\dev\github\pyro>reuse lint

# SUMMARY

* Bad licenses: 0
* Deprecated licenses: 0
* Licenses without file extension: 0
* Missing licenses: 0
* Unused licenses: 0
* Used licenses: BSD-3-Clause, MIT, CC0-1.0, Apache-2.0
* Read errors: 0
* Files with copyright information: 838 / 838
* Files with license information: 838 / 838

Congratulations! Your project is compliant with version 3.2 of the REUSE Specification :-)

[fritzo]

Thanks for your suggestion, but I'd rather avoid adding a dependency. make format seems to work fine. If you can argue reuse would reduce our maintenance overhead, then please open smaller, less invasive, more targeted PRs.