[RunroomSortableBehaviorBundle] Add Usage guide on the README

[dmitryuk]

• copied and modified some part of readme from pix package
• added section "Submitting a Pull Request or an Issue"

Also would be great to hide pull requests tab in https://github.com/Runroom/RunroomSortableBehaviorBundle, because you are a maintainer

[codecov[bot]]

Codecov Report

Merging #131 (5e2e1be) into master (26f9297) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #131      +/-   ##
============================================
- Coverage     99.16%   99.16%   -0.01%     
  Complexity      615      615              
============================================
  Files           159      159              
  Lines          2264     2262       -2     
============================================
- Hits           2245     2243       -2     
  Misses           19       19              

Impacted Files	Coverage Δ
...page-bundle/src/Repository/BasicPageRepository.php	100.00% <ø> (ø)
...es-bundle/src/Repository/CookiesPageRepository.php	100.00% <ø> (ø)
...ction-bundle/src/Repository/RedirectRepository.php	100.00% <ø> (ø)
...undle/src/Repository/MetaInformationRepository.php	100.00% <ø> (ø)
...on-bundle/src/Repository/TranslationRepository.php	100.00% <ø> (ø)
...es/user-bundle/src/Command/ActivateUserCommand.php	100.00% <ø> (ø)
.../user-bundle/src/Command/ChangePasswordCommand.php	100.00% <ø> (ø)
...ages/user-bundle/src/Command/CreateUserCommand.php	100.00% <ø> (ø)
.../user-bundle/src/Command/DeactivateUserCommand.php	100.00% <ø> (ø)
...e-behavior-bundle/src/Admin/SortableAdminTrait.php	100.00% <100.00%> (ø)
... and 2 more

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[jordisala1991]

I think it should be ok now. wdyt @dmitryuk ? I have improve a little bit your changes.

[jordisala1991]

I think it is a good start, Thank you @dmitryuk