Fix and update Installation guide

[kAIto47802]

Description

There are several incorrect statements in the optuna-dashbord installation guide:

• In the documentation, it is stated that after cloning the optuna-dashboard GitHub repository, one should move to the optuna directory. However, the correct directory to move to is optuna-dashboard.
• The compiling guide is outdated and inconsistent with the instructions in CONTRIBUTING.md.
• It says ``See CONTRIBUTING.md for more details,'' but the link points to the optuna repository's CONTRIBUTING.md. The correct link should be to the optuna-dashboard repository's CONTRIBUTING.md.

Additionally, the optuna-dashboard repository does not have an issue template for documentation-related issues. It might be helpful to add one.

How to Reproduce

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Python version

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Optuna version

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optuna-dashboard version or git revision

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Web browser

Google Chrome, Firefox, etc.

[c-bata]

Good catch! Thank you for reporting.

[c-bata]

Regarding the GitHub issue template, let me keep it as is. Because I would like to recommend to create pull requests rather than filing an issue.