Add example usage of log operation

[garvitgoel]

I have added an example of how to use the log operator in the debugging-operations.md file

[garvitgoel]

Hi @mmilenkovic , just bringing this PL to your attention.

[alrubio]

Your comment on the log instruction applies to all circom instructions, so I do not see it is necessary to explicitly say it for log.
We may add a general comment about all instructions if it is not said.

[alrubio]

If there is no further discussion I'll proceed to close the PR. Thanks for your comments.

[garvitgoel]

Yeah sure. I just made the suggestion since I myself lost time in figuring out this issue. I think example cases are very helpful while learning a new language.