Extend README and check config for inconsistencies with supervised Po…

…ST service (#5259)

## Motivation
This change adds additional information on how to setup a node with post service correctly and adds code to node startup that ensures a node with a valid 1.2.x config is able to start and smesh with 1.3.x

## Changes
- add upgrade information about post service to `CHANGELOG.md`
- add info on how to configure a node for post correctly in `README.md`
- add checks and auto-fixes to node startup

## Test Plan
- a test for the auto-fixes was added

## TODO
<!-- This section should be removed when all items are complete -->
- [x] Explain motivation or link existing issue(s)
- [x] Test changes and document test plan
- [x] Update documentation as needed
- [x] Update [changelog](../CHANGELOG.md) as needed

CHANGELOG.md

@@ -16,9 +16,18 @@ See [RELEASE](./RELEASE.md) for workflow instructions.
 
 ### Upgrade information
 
+This release is not backwards compatible with v1.2.x. Upgrading will change the node's database schema and
+migrate local state to a new database. The migration will take place at the first startup after the upgrade.
+Be aware that after upgrading you cannot downgrade to v1.2.x any more.
+
 Current release is expected to be adopted by majority of the network participants before epoch 11 starts.
 Nodes that do not update before epoch 11 risk their proposals being rejected by the rest of the network.
 
+This release is the first step towards separating PoST from the node. Proof generation is now done via a dedicated
+service. This service is started automatically by the node and is shut down when the node shuts down. In most
+setups this should work out of the box, but if you are running into issues please check the REAMDE.md file
+for more information on how to configure the node to work with the PoST service.
+
 ### Highlights
 
 ### Features
@@ -70,7 +79,7 @@ Nodes that do not update before epoch 11 risk their proposals being rejected by
 
   ```json
   "main": {
-      "prune-activesets-from": 4294967295
+    "prune-activesets-from": 4294967295
   }
   ```
 
@@ -93,6 +102,9 @@ Nodes that do not update before epoch 11 risk their proposals being rejected by
 
 * [#5209](https://github.com/spacemeshos/go-spacemesh/pull/5209) Removed API to update poet servers from SmesherService.
 
+* [#5259](https://github.com/spacemeshos/go-spacemesh/pull/5259) Node now tries to fix a 1.2.x config to be compatible with
+  1.3.x at startup.
+
 ## v1.2.0
 
 ### Upgrade information