[BUG] Reading configuration file from read-only filesystem fails.

[RobertZenz]

Describe the bug

When starting btop on a read-only filesystem (with a btop.conf present at the right location), btop complains that it can't find $HOME nor $XDG_CONFIG_HOME, the configuration file is not read and btop reverts to its defaults.

Remounting the filesystem as read-write allows btop to start with the correct configuration.

I guess this is related to #637.

To Reproduce

Have a read-only filesystem on which the configuration resides.

Expected behavior

btop should at least start with the configuration that is present, and then complain that it can't write changes to it.

[imwints]

Yeah, the current config check fails if $HOME or $XDG_CONFIG_HOME are not writable.

I have created a branch that should allow read only configuration files. I'd like you to test it before creating a PR.
It works on a read only tmpfs

[RobertZenz]

Yes, that does work as expected, thank you.

However, there is now no message at all that the configuration could not be saved, which isn't ideal either.

[imwints]

I've updated the branch, it now also warns if the config dir resides on a read only filesystem

[RobertZenz]

Neat! Thank you very much.