Hi i have an sobject in which a picklist with 3 values has been saved. Now i want to give additional values in picklist via a input text box in  visualforce and apex. I am able to fetch the records here. but unable to add values to it.  Adding my code for reference.

<apex:page controller="clientobject">
<apex:form >
 <apex:pageBlock >
  <apex:selectList id="countries" value="{!picklist}" size="1">
  <apex:selectOptions value="{!countries}"/>
</apex:selectList><br/><br/>
  Enter value to add:<apex:inputText value="{!pick}"/>
  <apex:commandButton value="add" />
 </apex:pageBlock>
</apex:form>
</apex:page>
//controller class
public class clientobject {
public string pick{set;get;}
public string picklist{set;get;}
transient List<Schema.PicklistEntry> ple = new List<Schema.PicklistEntry>();
public clientobject(){

}
public List<SelectOption> getCountries(){
  List<SelectOption> options = new List<SelectOption>();
        
   Schema.DescribeFieldResult fieldResult = OfficeLocation__c.Country__c.getDescribe();
  ple = fieldResult.getPicklistValues();
    
        
   for( Schema.PicklistEntry f : ple)
   {
 
      options.add(new SelectOption(f.getLabel(), f.getValue()));
      
   }       
    system.debug('picklist values are ::::::::::'+options);
   return options;
  }
 }

 i don't know how to perform dml actions on schema.describe calls ? Any suggestions would be appreciated