Fix headings in docs

Author: nop33

README.md

@@ -27,7 +27,7 @@ If nothing helps and you are stuck, these are places you can go ask for guidance
 
 ## Troubleshooting
 
-## Missing node signing public key
+### Missing node signing public key
 
 Restart the DFX network with:
 
@@ -37,7 +37,7 @@ dfx start --clean
 
 The --clean option removes checkpoints and stale state information from your project’s cache so that you can restart the Internet Computer replica and web server processes in a clean state.
 
-## How to upgrade the SDK
+### How to upgrade the SDK
 
 To upgrade from a previous SDK version, run: