[ReadMe] fix information about metrics history time

[Aratcho]

Describe the bug

1. In ReadMe file, there are paradoxal information about prometheus metrics used : default history time is whether 14 last days or 7 last days.

2. Also, related topic : in ReadMe file (https://github.com/robusta-dev/krr?tab=readme-ov-file#requirements) "Historic pods that no longer exist in the cluster will not be taken into consideration.", does it mean that, for a same deployment, if in the past couple of days, a new pod is created (as former one has been crashed) and is still present in the cluster, highest RAM value of the first pod will not been taken into account as it is not present in the cluster anymore ?

To Reproduce
Steps to reproduce the behavior for the first bug :

1. 14 days in : https://github.com/robusta-dev/krr?tab=readme-ov-file#difference-with-kubernetes-vpa
2. 7 days ("past week") in : https://github.com/robusta-dev/krr?tab=readme-ov-file#algorithm
3. --history_duration can be set, but what is default value ? : https://github.com/robusta-dev/krr?tab=readme-ov-file#usage

Expected behavior
I guess default history time is : 14 last days. ReadMe shall be clarified. Also with default values of each arguments in "Usage" section.

Are you interested in contributing a fix for this?
No.

Additional context
Add any other context about the problem here.

[jaikishanwadhawa]

got above output (it mentions default values) after running
krr simple --help