Correcting file name in the first example to match the texts
Minor updates to README.md

Updated the Issues URL because it is returning a 404 (not sure why .../blob/master/... was inserted). 

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Merge pull request #508 from AFBarstow/patch-1

Minor updates to README.md
Thanks!
Merge pull request #503 from eduardojmatos/patch-1

Correcting file name in the first example to match the texts
Thanks!
Add singular item
caches.get & caches.create becomes caches.open
Handle exiting active worker properly upon InstallEvent.replace() invocation. Fixes #364.