Add missing documetation for is:from-cache

[barryhunter]

is:from-cache was not documented.

Found it from https://stackoverflow.com/questions/34130116/how-to-filter-cached-requests-in-chrome-devtools

is:service-worker-initiated came from https://www.smashingmagazine.com/2021/02/useful-chrome-firefox-devtools-tips-shortcuts/

Fixes #SOME_ISSUE_NUMBER

Changes proposed in this pull request:

[chrome-devrel-infra[bot]]

:white_check_mark: Preview (static) for commit 34e46dc30e677f017dea3d9b2c123b125896419c available at https://pr-6252-static-dot-dcc-staging.uc.r.appspot.com/.

The following pages likely changed with this PR:

• https://pr-6252-static-dot-dcc-staging.uc.r.appspot.com/docs/devtools/network/reference/