emerge: update page (#15164)

* Add long options
* Replace `--unmerge` with `--depclean`, as suggested in the Gentoo
  wiki

pages/linux/emerge.md

@@ -10,7 +10,7 @@
 
 - Update all packages, including dependencies:
 
-`sudo emerge -uDNav @world`
+`sudo emerge {{-avuDN|--ask --verbose --update --deep --newuse}} @world`
 
 - Resume a failed updated, skipping the failing package:
 
@@ -18,16 +18,16 @@
 
 - Install a new package, with confirmation:
 
-`sudo emerge -av {{package}}`
+`sudo emerge {{-av|--ask --verbose}} {{package}}`
 
-- Remove a package, with confirmation:
+- Remove a package and its dependencies with confirmation:
 
-`sudo emerge -Cav {{package}}`
+`sudo emerge {{-avc|--ask --verbose --depclean}} {{package}}`
 
-- Remove orphaned packages (that were installed only as dependencies):
+- Remove orphaned packages (installed as dependencies but no longer required by any package):
 
-`sudo emerge -avc`
+`sudo emerge {{-avc|--ask --verbose --depclean}}`
 
 - Search the package database for a keyword:
 
-`emerge -S {{keyword}}`
+`emerge {{-S|--searchdesc}} {{keyword}}`