users.ini and podbot mm have nothing common. To get the remote access (rcon) of the server You have to type in Your client console:
rcon_password "yourpassword_from_server.cfg_on_the_server"
Then - if You got the access - try this:
rcon pb add 100
That's it.
Another way to control bots on the server is good explaind
here (and I'm not going to add there anything more). Just don't be lazy and read all 100 posts there.
Yet another possibility - without using rcon access and podbot mm build in podbotmenu - You can use
this plugin (if You are using AMXMODX).