We should not use spaces or underscore in repository/file name.

[adityaramteke]

The reason for denying spaces are relatively clear - if a repository name can never have space, then any code generation that generates a reference to the repository never has to apply a quoting rule to the canonical description of the reference and the resulting reference will always be parsed correctly.

For example, repo 'Administrator Guide', then the HTTP URL of the repo would have to be generated as https://docs.gluster.org/en/latest/Administrator%20Guide/ which would be generated like https://docs.gluster.org/en/latest/Administrator Guide/

However, if spaces are simply not allowed in repository names in the first place, then a literal copy of the canonical repository name https://docs.gluster.org/en/latest/Administrator-Guide/ will always be correct in any context it is used and no-one - GitHub, 3rd party script writers, or yourself - will have to spend any effort to ensure that quoting rules are applied correctly in every circumstance that they may be required.

So, while in principle it would be technically possible to allow spaces in repository names, the primarily aesthetic of doing so probably weren't considered to be worth the significant amount of engineering effort that would be required to support it properly and consistently.