Add link to documentation for root packages with no go files

[LandonTClipp]

Description

There appears to be a limitation with the go package parser when you attempt to load a package with no files. I can't find a way to get information about where the package is located on-disk unless at least 1 go file exists. I added docs that explain this case and linked to it in the logs.

02 Jun 23 12:30 EDT ERR package contains no go files error="no go files found in root search path" documentation=https://vektra.github.io/mockery/notes/#error-no-go-files-found-in-root-search-path dry-run=false package-path=github.com/vektra/mockery/v2/pkg/fixtures/pkg_with_no_files version=v0.0.0-dev

• Fixes Package config with recursive option on folder with only sub-folders: index out of range error #611
• Fixes Generate mocks before unit tests run #631
• error: `no go files found in root search path` #636

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Version of Golang used when building/testing:

• 1.11
• 1.12
• 1.13
• 1.14
• 1.15
• 1.16
• 1.17
• 1.18
• 1.19
• 1.20

How Has This Been Tested?

Unit tests

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes