doc/jsonrpc: fix up nvmf_subsystem_remove_ns

- Add missing ~~~ to close the code section
- Fix grammar

Change-Id: I8ce5ab3ef33962cbb766a4ee4caf26f23f3bef1e
Fixes: d9321520ce02 ("nvmf: add Namespace deletion RPC support")
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/404964
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

doc/jsonrpc.md

@@ -425,7 +425,7 @@ Example response:
 
 ## nvmf_subsystem_remove_ns method {#rpc_nvmf_subsystem_remove_ns}
 
-Remove a namespace to a subsystem.
+Remove a namespace from a subsystem.
 
 ### Parameters
 
@@ -458,6 +458,7 @@ Example response:
   "id": 1,
   "result": true
 }
+~~~
 
 ## nvmf_subsystem_add_host method {#rpc_nvmf_subsystem_add_host}