Update docs for latest Cosmos SDK version

We recently expunged Pulsar from our repo (yay!). In the process, we
needed to upgrade to the next patch version of the Cosmos SDK (v0.50.8).

Version v0.50.8 has dependencies on modules that rely on `gogoproto`'s
`MergedRegistry` function. Thus, it's not possible to comment out the
line (as we were doing [before]), unless we wanted to multiply the
number of `go replace` directives.

Instead, we address the root cause in the `go-libp2p` package. That's
the only new replace directive we need. We have [upstreamed the fix],
but that may not be used by the op-node for quite some time. A single
`replace` is fine for now.

This commit updates the docs with the correct instructions for the
latest Monomer changes.

[before]: https://github.com/polymerdao/monomer/blob/c7ecbee46914c943bfbecaf2bd5ded3076df09f2/doc/docs/learn/create-an-app-with-monomer.md?plain=1#L150
[upstreamed the fix]: libp2p/go-libp2p#2920

doc/docs/learn/create-an-app-with-monomer.md

@@ -22,7 +22,7 @@ We'll use the handy tool [spawn](https://github.com/rollchains/spawn) to bootstr
 ```bash
 git clone https://github.com/rollchains/spawn
 cd spawn
-git checkout v0.50.4
+git checkout v0.50.5
 make install
 ```
 </details>
@@ -35,7 +35,7 @@ spawn new rollchain --consensus=proof-of-authority \
     --bech32=roll \
     --denom=uroll \
     --bin=rolld \
-    --disabled=cosmwasm,globalfee \
+    --disabled=cosmwasm,globalfee,block-explorer \
     --org=monomer
 ```
 
@@ -47,7 +47,6 @@ Let's move into the `rollchain` directory and add Monomer to our application.
 
 ```bash
 cd rollchain
-go get github.com/polymerdao/monomer
 ```
 
 ### Import `x/rollup` and `x/testmodule`
@@ -142,26 +141,6 @@ rollup.NewAppModule( // <-- add this block
 testmodule.New(testmodulekeeper.New(runtime.NewKVStoreService(keys[testmodule.StoreKey]))),
 ```
 
-### Finalizing our Changes
-Near the bottom of the `NewChainApp` function, comment out the following lines:
-```go
-// app/app.go
-
-/*protoFiles, err := proto.MergedRegistry()
-if err != nil {
-    panic(err)
-}
-err = msgservice.ValidateProtoAnnotations(protoFiles)
-if err != nil {
-    // Once we switch to using protoreflect-based antehandlers, we might
-    // want to panic here instead of logging a warning.
-    _, _ = fmt.Fprintln(os.Stderr, err.Error())
-}*/
-```
-and remove this import: `github.com/cosmos/cosmos-sdk/types/msgservice`. 
-
-
-
 That's it for `app.go`! Next we'll add a CLI command to interact with Monomer.
 
 ### Defining the Monomer Command
@@ -206,10 +185,16 @@ func initRootCmd(
 ```
 
 ## Building the Application
-Before we can build our application, we need to add the following replace directive in `go.mod` and then run `go mod
+Before we can build our application, we need to add the following replace directives in `go.mod` and then run `go mod
 tidy`: 
 ```go
 github.com/ethereum/go-ethereum => github.com/joshklop/op-geth v0.0.0-20240515205036-e3b990384a74
+github.com/libp2p/go-libp2p => github.com/joshklop/go-libp2p v0.0.0-20240814165419-c6b91fa9f263
+```
+
+and change the `cosmossdk.io/core` replace directive to `v0.11.1`:
+```
+cosmossdk.io/core => cosmossdk.io/core v0.11.1
 ```
 
 Now we can build our application by running