Expand "Specify process types" page

[hyounes4560]

Summary

We need to rewrite/update the Specify process types. The updated page should follow a similar structure as seen in the exec.d binaries page.

What questions should this documentation answer?

Who is the target audience for this documentation?

• [ ] App Developer
• [x] Buildpack Author
• [ ] Operator
• [ ] Other:

Additional Information

[hyounes4560]

@AidanDelaney Could you please attach any content/examples that could be added to the updated page? Thanks