docs: how to add tm version to RPC (#6151)

## Description

Add docs on how to get tendermint version into RPC version outputs

docs/tendermint-core/rpc.md

@@ -9,3 +9,19 @@ The RPC documentation is hosted here:
 - [https://docs.tendermint.com/master/rpc/](https://docs.tendermint.com/master/rpc/)
 
 To update the documentation, edit the relevant `godoc` comments in the [rpc/core directory](https://github.com/tendermint/tendermint/tree/master/rpc/core).
+
+If you are using Tendermint in-process, you will need to set the version to be displayed in the RPC.
+
+If you are using a makefile with your go project, this can be done by using sed and `ldflags`.
+
+Example: 
+
+```
+VERSION := $(shell go list -m github.com/tendermint/tendermint | sed 's:.* ::')
+LD_FLAGS = -X github.com/tendermint/tendermint/version.TMCoreSemVer=$(VERSION)
+
+install:
+  @echo "Installing the brr machine"
+  @go install -mod=readonly -ldflags "$(LD_FLAGS)" ./cmd/<app>
+.PHONY: install
+```