docs: add an UPDATE.md file for additional steps

Former-commit-id: 1e9bbcfda11a9bd3bc47523396a4663b03ba33a7

UPDATE.md

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+This document describes eventual additional steps that might be required to update between two versions of Kong. If nothing is described here for a particular version and platform, then assume the update will go smoothly.
+
+## Update to Kong `0.3.x`
+
+Kong now requires a patch on OpenResty for SSL support. On Homebrew you will need to reinstall OpenResty.
+
+#### Homebrew
+
+```shell
+$ brew update
+$ brew reinstall mashape/kong/ngx_openresty
+$ brew upgrade kong
+```
+
+#### Troubleshoot
+
+If you are seeing a similar error on `kong start`:
+
+```
+nginx: [error] [lua] init_by_lua:5: Startup error: Cassandra error: Failed to prepare statement: "SELECT id FROM apis WHERE path = ?;". Cassandra returned error (Invalid): "Undefined name path in where clause ('path = ?')"
+```
+
+You can run the following command to update your schema:
+
+```
+$ kong migrations up
+```
+
+Please consider updating to `0.3.1` or greater which automatically handles the schema migration.