Added a note about changing pinentry methods and saving. For example,

Added a note about changing pinentry methods and saving. For example,
doing a pwmd_open2() will send "OPTION PINENTRY=0" to the server. Doing
a pwmd_save() after this will cause the SAVE command to be sent
without a passphrase and pwmd won't care because it's pinentry is
disabled and it assumes this is what you want (an empty passphrase).
"OPTION PINENTRY=1" must be sent before calling the save function for
pwmd to use it's own pinentry again.