security: add more examples (#6645)

pages/osx/security.md

@@ -13,4 +13,12 @@
 
 - Create a keychain:
 
-`security create-keychain -p {{password}} {{name.keychain}}`
+`security create-keychain -p {{password}} {{keychain.name}}`
+
+- Set a certificate to use with a website or [s]ervice by its [c]ommon name (fails if several certificates with the same common name exist):
+
+`security set-identity-preference -s {{URL|hostname|service}} -c "{{common_name}}" {{path/to/file.keychain}}`
+
+- Add a certificate from file to a [k]eychain (if -k isn't specified, the default keychain is used):
+
+`security add-certificates -k {{keychain.name}} {{path/to/file.pem}}`