Add docs to describe how to compile git with libpcre2

What does this MR do?

addresses: gitaly#1214 (closed)

We are making libpcre2 a hard requirement for git. Most of the distro provided git ship with libpcre2, but in the case that it doesn't, we want to provide instructions on how to build it from source. (gitaly#1214 (comment 75857692))

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team