<ins> and <del> tag don't work in plugin readme

[MocioF]

Even if <ins> and <del> tag should be supported by readme's markdown:
$block_tags_a_re = 'ins|del';

they don't work in plugin's readme and are replaced with ''.

[dd32]

@MocioF What's an example use-case for these tags? To sure that we have appropriate styling for them.

[MocioF]

As an example:
Looking at National Vulnerability Database ran by US NIST, *more than <del>1,600</del> <ins>900 (March 2024)</ins> vulnerabilities* are reported as [XSS for Wordpress' plugins and themes](https://nvd.nist.gov/vuln/search#/nvd/home?keyword=XSS%20Wordpress&resultType=records).

Looking at National Vulnerability Database ran by US NIST, more than 1,600 900 (March 2024) vulnerabilities are reported as XSS for Wordpress' plugins and themes.

[dd32]

An example of how it's useful to plugins... :) So we know how to properly style these tags..