add `OLLAMA_KEEP_ALIVE` to environment variable docs for `ollama serve` (#3127)

cmd/cmd.go

@@ -970,9 +970,10 @@ func NewCLI() *cobra.Command {
 	serveCmd.SetUsageTemplate(serveCmd.UsageTemplate() + `
 Environment Variables:
 
-    OLLAMA_HOST       The host:port to bind to (default "127.0.0.1:11434")
-    OLLAMA_ORIGINS    A comma separated list of allowed origins.
-    OLLAMA_MODELS     The path to the models directory (default is "~/.ollama/models")
+    OLLAMA_HOST         The host:port to bind to (default "127.0.0.1:11434")
+    OLLAMA_ORIGINS      A comma separated list of allowed origins.
+    OLLAMA_MODELS       The path to the models directory (default is "~/.ollama/models")
+    OLLAMA_KEEP_ALIVE   The duration that models stay loaded in memory (default is "5m")
 `)
 
 	pullCmd := &cobra.Command{