Add metric section in usage documentation

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.88%. Comparing base (cb99489) to head (9d97c8d). Report is 1 commits behind head on releases/1.1.0.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## releases/1.1.0 #75 +/- ## ================================================== + Coverage 93.82% 93.88% +0.05% ================================================== Files 28 28 Lines 1896 1897 +1 ================================================== + Hits 1779 1781 +2 + Misses 117 116 -1 ``` | [Flag](https://app.codecov.io/gh/openvinotoolkit/openvino_xai/pull/75/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit) | Coverage Δ | | |---|---|---| | [dev-py310](https://app.codecov.io/gh/openvinotoolkit/openvino_xai/pull/75/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit) | `93.88% <100.00%> (+0.05%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openvinotoolkit#carryforward-flags-in-the-pull-request-comment) to find out more.

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[GalyaZalesskaya]

@goodsong81 Let's add table with numbers in a separate PR, once they're ready. Should it be in README, Usage.MD or somewhere else, what do you think?

[goodsong81]

@goodsong81 Let's add table with numbers in a separate PR, once they're ready. Should it be in README, Usage.MD or somewhere else, what do you think?

Somewhere in the "Methods" section in the user guide would be a good choice. Not sure of README.md. @negvet Do you have any preferences?