Update docs

[johnfercher]

Description

Related Issue

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
• Updated README.md
• Executed make examples to update all examples inside docs/examples.
• New public methods/structs/interfaces has comments upside them explaining they responsibilities
• Executed make dod with none issues pointed out by golangci-lint

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (36939c4) 79.89% compared to head (b6c2d65) 79.89%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #381   +/-   ##
=======================================
  Coverage   79.89%   79.89%           
=======================================
  Files          61       61           
  Lines        2018     2018           
=======================================
  Hits         1612     1612           
  Misses        378      378           
  Partials       28       28           

Flag	Coverage Δ
unittests	79.89% <ø> (ø)

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