update readme and cmd usage comments

README.md

@@ -286,21 +286,25 @@ The config provides information for composing a set of transformers:
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer2]
         path = "path/to/transformer2"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "2"
     [exporter.transformer3]
         path = "path/to/transformer3"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer4]
         path = "path/to/transformer4"
         type = "eth_storage"
         repository = "github.com/account2/repo2"
         migrations = "to/db/migrations"
+        rank = "1"
 ```
 - `home` is the name of the package you are building the plugin for, in most cases this is github.com/vulcanize/vulcanizedb
 - `name` is the name used for the plugin files (.so and .go)   
@@ -316,6 +320,12 @@ The config provides information for composing a set of transformers:
         - `eth_event` indicates the transformer works with the [event watcher](https://github.com/vulcanize/maker-vulcanizedb/blob/staging/libraries/shared/watcher/event_watcher.go)
          that fetches event logs from an ETH node
     - `migrations` is the relative path from `repository` to the db migrations directory for the transformer
+    - `rank` determines the order that migrations are ran, with lower ranked migrations running first
+        - this is to help isolate any potential conflicts between transformer migrations
+        - start at "0" 
+        - use strings
+        - don't leave gaps
+        - transformers with identical migrations/migration paths should share the same rank
 - Note: If any of the imported transformers need additional config variables those need to be included as well   
 
 This information is used to write and build a Go plugin which exports the configured transformers.

cmd/compose.go

@@ -59,21 +59,25 @@ var composeCmd = &cobra.Command{
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer2]
         path = "path/to/transformer2"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "2"
     [exporter.transformer3]
         path = "path/to/transformer3"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer4]
         path = "path/to/transformer4"
         type = "eth_storage"
         repository = "github.com/account2/repo2"
         migrations = "to/db/migrations"
+        rank = "1"
 
 
 Note: If any of the plugin transformer need additional
@@ -149,6 +153,10 @@ func prepConfig() {
 		if !mrOK || mr == "" {
 			log.Fatal(name, "transformer config is missing `rank` value")
 		}
+		rank, err := strconv.Atoi(mr)
+		if err != nil {
+			log.Fatal(name, "migration `rank` can't be converted to an integer")
+		}
 		t, tOK := transformer["type"]
 		if !tOK {
 			log.Fatal(name, "transformer config is missing `type` value")
@@ -157,10 +165,6 @@ func prepConfig() {
 		if transformerType == config.UnknownTransformerType {
 			log.Fatal(errors.New(`unknown transformer type in exporter config accepted types are "eth_event", "eth_storage"`))
 		}
-		rank, err := strconv.Atoi(mr)
-		if err != nil {
-			log.Fatal(name, "migration `rank` can't be converted to an integer")
-		}
 
 		transformers[name] = config.Transformer{
 			Path:           p,

cmd/composeAndExecute.go

@@ -59,21 +59,25 @@ var composeAndExecuteCmd = &cobra.Command{
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer2]
         path = "path/to/transformer2"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "2"
     [exporter.transformer3]
         path = "path/to/transformer3"
         type = "eth_event"
         repository = "github.com/account/repo"
         migrations = "db/migrations"
+        rank = "0"
     [exporter.transformer4]
         path = "path/to/transformer4"
         type = "eth_storage"
         repository = "github.com/account2/repo2"
         migrations = "to/db/migrations"
+        rank = "1"
 
 
 Note: If any of the plugin transformer need additional