Update custom-linux-kernel.md (punctuation, open-source, ...)

[SergeCroise]

• punctuation
• open-source (as an adjective)

Author checklist (Completed by original Author)

• Good fit for the Rocky Linux project? Title and Author Metatags inserted ?
• If applicable, steps and instructions have been tested to work
• Initial self-review to fix basic typos and grammar completed

Rocky Documentation checklist (Completed by Rocky team)

• 1st Pass (Document is good fit for project and author checklist completed)
• 2nd Pass (Technical Review - check for technical correctness)
• 3rd Pass (Detailed Editorial Review and Peer Review)
• Final approval (Final Review)

[SergeCroise]

hi @wsoyinka , please review!

[github-actions]

Test results for ebc9beb:

Number of broken URLs: 5

URL,RESULT,FILENAME
 http://www.modsecurity.org/,failed,guides/web/apache_hardened_webserver/modsecurity.md
 https://ersei.saggis.com/,failed,guides/contribute/README.md
 http://www.flaviosiqueira.com.br/,failed,guides/contribute/README.md
 https://github.com/andrewthiesen,failed,guides/contribute/README.md
 https://github.com/bdacus01,failed,guides/contribute/README.md