docs(ssh-agent): macOS and p10k advices (#11612)

plugins/ssh-agent/README.md

@@ -99,6 +99,33 @@ ssh-add -K -c -a /run/user/1000/ssh-auth <identities>
 
 For valid `ssh-add` arguments run `ssh-add --help` or `man ssh-add`.
 
+### Powerline 10k specific settings
+
+Powerline10k has an instant prompt setting that doesn't like when this plugin
+writes to the console. Consider using the following settings if you're using
+p10k (documented above):
+
+```
+zstyle :omz:plugins:ssh-agent quiet yes
+zstyle :omz:plugins:ssh-agent lazy yes
+```
+
+### macOS specific settings
+
+macOS supports using passphrases stored in the keychain when adding identities
+to the ssh-agent.
+
+```
+ssh-add --apple-use-keychain ~/.ssh/id_rsa ...
+```
+
+
+This plugin can be configured to use the keychain when loading using the following:
+
+```
+zstyle :omz:plugins:ssh-agent ssh-add-args --apple-load-keychain
+```
+
 ## Credits
 
 Based on code from Joseph M. Reagle: https://www.cygwin.com/ml/cygwin/2001-06/msg00537.html