Documentation on contributing

[butuzov]

This PR fix the reference to govet in contributing docs as linter that has one option. Not critical, just cleaning.

[ldez]

Hello,

could you explain a bit more the change?

sorry, didn't see that tit was changed from covet to unparam

[SVilgelm]

@butuzov Yeah, could you please explain why did you change the example from govet to unparam? I really don't see a reason to make this change

[butuzov]

Hi Guys.

I had run into an issue yesterday, that govet hasn't reported for shadoowing variables/packages. That snowballed into some investigation and this PR one of the outcomes.

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This is minor change to the website docs and can be left in place, but I guess we will skip the initial frustration of the person reading at the website "For example, govet has only 1 option: check-shadowing.", then looking to the GovetSettings struct and finding that there are more. I have looked for the next linter that has only one setting (that can be passed via CLI flag).

What I have missed is that there is another option for unparam (one not passed to CLI. So here are the options we have:

1. Replace govet with other linter with only one setting (next in the list is nakedret)
2. Close this issue and left govet in tutorial as "linter with only one option"/s

[butuzov]

Again, this quite a minor thing, and not critical.

[ldez]

LGTM