Move/positive decimal regex

[WillemZeiler]

PR Description:

Update and move Allow positive and decimal values.js
Moved the file to the Regex folder.
Refactored the code:

• use clearValue instead of setValue ''.
• fieldName to make it easier to adjust and use.
• Include comment to describe the Regex

Update and move readme.md
Moved the readme and made the text more descriptive. Included a description of what the validation actually does.

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[kmxo]

Sounds good.