Merge from oc-preview-docs-release: docs: Added note that INSTALL_SHORTCUT is...

Merge from oc-preview-docs-release: docs: Added note that INSTALL_SHORTCUT is implicit broadcast as of O.

The INSTALL_SHORTCUT broadcast is now a private, implicit broadcast,
so app developers should pin a shortcut themselves using the methods
in the ShortcutManager class on Android O and higher. Updated
manifest permission doc accordingly.

Test: make ds-docs
Bug: 36442658
Change-Id: I1777dfde691089485dc4e6b7cb8a9de0ee527298
Original-Change-Id: I0ef5595e2f08efbab6c28af5fa2f6b6c2295424c