[AppSec] Add note to docs on hub_branch parameter.

[lva-itscope]

[AppSec] Add note to docs on hub_branch parameter.

[LaurenceJJones]

I think the AppSec Installation section could be improved by adding the information that inside config.yaml hub_branch might need to be changed. Since the default value is the wip_lapi branch which does not have the appsec collections mentioned in the docs, a note could be useful here.

I am referring to a problem I described on the forum here.

crowdsec-docs/crowdsec-docs/docs/appsec/installation.md

Line 42 in 588a817

## Initialize AppSec configuration and rules

Good find! Honestly we shouldn't call it the "default configuration" as it doesn't actually match the one we ship by default so we should update the "default" to be the actual default which omits that configuration as by default crowdsec will attempt to find the branch associated with the version.

[lva-itscope]

After further looking into it I also realized, that the "default configuration" is not really the default configuration.
And my error was caused because I used the default config as base for my custom one, so I had all the fields in it not just the ones I wanted to override.