Update README.md to fix link to the docs

[oruebel]

Fix #311

[codecov[bot]]

Codecov Report

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

Comparison is base (28418b3) 66.24% compared to head (fe0a42c) 66.24%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #312 +/- ## ======================================= Coverage 66.24% 66.24% ======================================= Files 35 35 Lines 3478 3478 ======================================= Hits 2304 2304 Misses 1174 1174 ``` | [Flag](https://app.codecov.io/gh/NeurodataWithoutBorders/nwbwidgets/pull/312/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NeurodataWithoutBorders) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/NeurodataWithoutBorders/nwbwidgets/pull/312/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NeurodataWithoutBorders) | `66.24% <ø> (ø)` | | 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=NeurodataWithoutBorders#carryforward-flags-in-the-pull-request-comment) to find out more.

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