Update docs

[johnfercher]

Description

• Update docs

Related Issue

386

Checklist

check with "x", if applied to your change

• [ ] All methods associated with structs has func (<first letter of struct> *struct) method() {} name style.
• [ ] Wrote unit tests for new/changed features.
• [ ] Followed the unit test when,should naming pattern.
• [ ] Updated docs/doc.go and docs/*
• [ ] Updated pkg/pdf/example_test.go
• [x] Updated README.md
• [ ] Executed make examples to update all examples inside docs/examples.
• [x] New public methods/structs/interfaces has comments upside them explaining they responsibilities
• [x] Executed make dod with none issues pointed out by golangci-lint

[codecov[bot]]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (d41c6cb) 79.84% compared to head (2520f5c) 79.84%.

Files	Patch %	Lines
pkg/components/page/page.go	12.50%	7 Missing :warning:
pkg/config/builder.go	76.20%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #389 +/- ## ======================================= Coverage 79.84% 79.84% ======================================= Files 61 61 Lines 2018 2018 ======================================= Hits 1611 1611 Misses 379 379 Partials 28 28 ``` | [Flag](https://app.codecov.io/gh/johnfercher/maroto/pull/389/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=John+Fercher) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/johnfercher/maroto/pull/389/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=John+Fercher) | `79.84% <85.00%> (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=John+Fercher#carryforward-flags-in-the-pull-request-comment) to find out more.

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