Add documentation of custom grok patterns

[Marusyk]

Context

The support of custom grok patterns was added in #15

Just add the directory with the name Patterns and a file (the file name doesn't matter) with your own patterns.

Like Patterns\grok-custom-patterns:

ZIPCODE [1-9]{1}[0-9]{2}\s{0,1}[0-9]{3}

and use:

Grok grok = new Grok("%{ZIPCODE:zipcode}:%{EMAILADDRESS:email}");
var grokResult = grok.Parse($"122001:[email protected]");

DoD

Describe a new feature in README

[ManasviGoyal]

@Marusyk can you pls elaborate? would like to work in this

[Marusyk]

Hi @ManasviGoyal please go ahead. It is yours

[ManasviGoyal]

Can you help me get started? @Marusyk

[Marusyk]

@ManasviGoyal here is everything you need. Other information is in README.md. What other help do you need?
Also see, https://github.com/Marusyk/grok.net/blob/main/CONTRIBUTING.md

[obinnadtq]

Hi, please can I try working on this as well?

[ManasviGoyal]

Hi @ManasviGoyal please go ahead. It is yours

@Marusyk so i just have to describe this feature in the Read me file, right?

[Marusyk]

@ManasviGoyal right

@obinnadtq yes, if @ManasviGoyal doesn't mind

[ManasviGoyal]

@Marusyk pls check