Add troubleshooting steps for local setup issues (solves/32193)

[sundaram2021]

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[sundaram2021]

I have added troubleshooting guide for the issue we get while setting up the gitea repo locally after forking

problem looks like this

solution
1.

2.

And It solves the problem

[lunny]

Please send the pull request to docs repository. https://gitea.com/gitea/docs