[feature request] improve the document of tutorial/kruise-install.md

[AaronLinOops]

What would you like to be added:
for this document, tutorial/kruise-install.md
troubleshooting steps is needed to find out why the endpoint is empty.

Why is this needed:
it is a common problem easy to encountered

[FillZpp]

@linwukang The endpoint might be empty because kruise-manager remain starting.
We have remove the default leader election in #50 , so kruise should start faster now.

[jian-he]

@linwukang close this issue based on comment above, let us know if you still run into the same issues.