Add README steps to upgrade Timesketch DB

[jkppr]

This PR adds a section in the Timesketch charts readme file explaining how to perform Database upgrades for the kubernetes deployment when required by the new Timesketch release.

[jkppr]

Failing test:

Deleting outdated charts
Linting chart "timesketch => (version: \"1.0.5\", path: \"charts/timesketch\")"
Checking chart "timesketch => (version: \"1.0.5\", path: \"charts/timesketch\")" for a version bump...
Old chart version: 1.0.5
Error: failed linting charts: failed processing charts
New chart version: 1.0.5

@wajihyassine Given I only updated documentation and not the charts, should this still be bumped?

[wajihyassine]

LGTM, thank you for the changes!

[wajihyassine]

Failing test:

Deleting outdated charts
Linting chart "timesketch => (version: \"1.0.5\", path: \"charts/timesketch\")"
Checking chart "timesketch => (version: \"1.0.5\", path: \"charts/timesketch\")" for a version bump...
Old chart version: 1.0.5
Error: failed linting charts: failed processing charts
New chart version: 1.0.5

@wajihyassine Given I only updated documentation and not the charts, should this still be bumped?

So I thought that was the case, but issue template needs to be updated it doesn't look like the chart-testing knows how to differentiate certain files while including it into the packaged chart still helm/chart-testing#530. Need to look into either updating the issue template or finding a way to update exclude *.md files

For this case can you bump the version number and then run helm dependency update and then should be good to merge.