Adding usage string

[nsomar]

Adding usage string.

Now the command will set the usage when calling helpMessage
The name of the command will be the first string in the usage

For example, for usage show origin-name
The command name is show

When displaying the help we will have:

Usage:
  git remote show origin-name

@goyox86

[codecov-io]

Current coverage is 95.01% (diff: 95.85%)

Merging #36 into master will increase coverage by 0.04%

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+ Hits           2041       2174   +133   
- Misses          108        114     +6   
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[nsomar]

@goyox86 merging this now