Start upgrade docs

UPGRADING.md

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+# Upgrading
+
+With stargate, we have access to the `x/upgrade` module, which we can use to perform
+inline upgrades. Please first read both the basic 
+[x/upgrade spec](https://github.com/cosmos/cosmos-sdk/blob/master/x/upgrade/spec/01_concepts.md)
+and [go docs](https://godoc.org/github.com/cosmos/cosmos-sdk/x/upgrade#hdr-Performing_Upgrades)
+for the background on the module.
+
+In this case, we will demo an update with no state migration. This is for cases when
+there is a state-machine-breaking (but not state-breaking) bugfix or enhancement.
+There are some
+[open issues running some state migrations](https://github.com/cosmos/cosmos-sdk/issues/8265)
+and we will wait for that to be fixed before trying those.
+
+The following will lead through running an upgrade on a local node, but the same process
+would work on a real network (with more ops and governance coordination).
+
+## Setup
+
+We need to have two different versions of `wasmd` which depend on state-compatible
+versions of the Cosmos SDK. We only focus on upgrade starting with stargate. You will
+have to use the "dump state and restart" approach to move from launchpad to stargate.
+
+For this demo, we will show an upgrade to our Musselnet going from `v0.12.1` to
+`v0.14.0`.
+
+### Handler
+
+You will need to register a handler for the upgrade. This is specific to a particular
+testnet and upgrade path, and the default `wasmd` will never have a registered handler
+on master. In this case, we make a `musselnet` branch off of `v0.14.0` just
+registering one handler with a given name. 
+
+Look at [PR 351](https://github.com/CosmWasm/wasmd/pull/351/files) for an example
+of a minimal handler. We do not make any state migrations, but rather use this
+as a flag to coordinate all validators to stop the old version at one height, and
+start the specified v2 version on the next block.
+
+### Prepare binaries
+
+Let's get the two binaries we want to test, the pre-upgrade and the post-upgrade
+binaries. In this case the pre-release is already a published to docker hub and
+can be downloaded simply via:
+
+`docker pull cosmwasm/wasmd:v0.12.1`
+
+The post-release is not published, so we can build it ourselves. Check out this
+`wasmd` repo, and the proper `musselnet` branch:
+
+```
+# use musselnet-v2 tag once that exists
+git checkout musselnet
+docker build . -t wasmd:musselnet-v2
+```
+
+Verify they are both working for you locally:
+
+```
+docker run cosmwasm/wasmd:v0.12.1 wasmd version
+docker run wasmd:musselnet-v2 wasmd version
+```
+
+## Start the pre-release chain
+
+Follow the normal setup stage, but in this case we will want to have super short
+governance voting period, 5 minutes rather than 2 days (or 2 weeks!).
+
+**Setup a client with private key**
+
+```sh
+## TODO: I think we need to do this locally???
+docker volume rm -f musselnet_client
+
+docker run --rm -it \
+    -e PASSWORD=1234567890 \
+    --mount type=volume,source=musselnet_client,target=/root \
+    cosmwasm/wasmd:v0.12.1 /opt/setup_wasmd.sh
+
+# enter "1234567890" when prompted
+docker run --rm -it \
+    --mount type=volume,source=musselnet_client,target=/root \
+    cosmwasm/wasmd:v0.12.1 wasmd keys show -a validator
+# use the address returned above here
+CLIENT=wasm1anavj4eyxkdljp27sedrdlt9dm26c8a7a8p44l
+```
+
+**Setup the blockchain node**
+
+```sh
+docker volume rm -f musselnet
+
+# add your testing address here, so you can do something with the client
+docker run --rm -it \
+    --mount type=volume,source=musselnet,target=/root \
+    cosmwasm/wasmd:v0.12.1 /opt/setup_wasmd.sh $CLIENT
+
+# Update the voting times in the genesis file
+docker run --rm -it \
+    --mount type=volume,source=musselnet,target=/root \
+    cosmwasm/wasmd:v0.12.1 sed -ie 's/172800s/300s/' /root/.wasmd/config/genesis.json
+
+# This will start both wasmd and rest-server, only rest-serve output is shown on the screen
+docker run --rm -it -p 26657:26657 -p 26656:26656 -p 1317:1317 \
+    --mount type=volume,source=musselnet,target=/root \
+    cosmwasm/wasmd:v0.12.1 /opt/run_wasmd.sh
+```
+
+## Sanity checks
+
+**TODO** move some tokens around
+
+## Vote on the upgrade
+
+**TODO**
+
+## Swap out binaries
+
+**TODO**
+
+## Check final state
+
+**TODO** Same balances in the final one