Feat(example): limit the number of keys per pool at each run

pools/example.org/local.conf

 # Local configuration for the example.org vanity pool
 # Parameters defined here will override those in the main config.
 
+# Limit the number of keys per pool at each run
+MKP224O_RUN_FLAGS="$MKP224O_RUN_FLAGS -n 5"
+
 # Ensure that regex support is enabled
 MKP224O_BUILD_FLAGS="--enable-intfilter=native --enable-regex=yes"