Adding troubleshooting section on mac installation

This troubleshooting section gathers information found on issue #38 on
GitExtensionsDocs while installing mac version of GitExtensions.

fixing typos and words after review

fixing another typo
fixing Git Extensions and Git download link
Merge pull request #49 from fraga/updateMacDoc2

Adding troubleshooting section on mac installation
Merge branch 'release/2.46' into release/2.47