Add warning to the sample config about bootstrap section (patroni#2925)

often people are trying to change it and coming with the questions why it doesn't work.

postgres0.yml

@@ -43,9 +43,13 @@ etcd:
 #  - 127.0.0.1:2223
 #  - 127.0.0.1:2224
 
+# The bootstrap configuration. Works only when the cluster is not yet initialized.
+# If the cluster is already initialized, all changes in the `bootstrap` section are ignored!
 bootstrap:
-  # this section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
-  # and all other cluster members will use it as a `global configuration`
+  # This section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
+  # and all other cluster members will use it as a `global configuration`.
+  # WARNING! If you want to change any of the parameters that were set up
+  # via `bootstrap.dcs` section, please use `patronictl edit-config`!
   dcs:
     ttl: 30
     loop_wait: 10

postgres1.yml

@@ -43,9 +43,13 @@ etcd:
 #  - 127.0.0.1:2222
 #  - 127.0.0.1:2224
 
+# The bootstrap configuration. Works only when the cluster is not yet initialized.
+# If the cluster is already initialized, all changes in the `bootstrap` section are ignored!
 bootstrap:
-  # this section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
-  # and all other cluster members will use it as a `global configuration`
+  # This section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
+  # and all other cluster members will use it as a `global configuration`.
+  # WARNING! If you want to change any of the parameters that were set up
+  # via `bootstrap.dcs` section, please use `patronictl edit-config`!
   dcs:
     ttl: 30
     loop_wait: 10

postgres2.yml

@@ -43,9 +43,13 @@ etcd:
 #  - 127.0.0.1:2222
 #  - 127.0.0.1:2223
 
+# The bootstrap configuration. Works only when the cluster is not yet initialized.
+# If the cluster is already initialized, all changes in the `bootstrap` section are ignored!
 bootstrap:
-  # this section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
-  # and all other cluster members will use it as a `global configuration`
+  # This section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
+  # and all other cluster members will use it as a `global configuration`.
+  # WARNING! If you want to change any of the parameters that were set up
+  # via `bootstrap.dcs` section, please use `patronictl edit-config`!
   dcs:
     ttl: 30
     loop_wait: 10