Add space not found doc

Add page about solving space not found problem

Closes #142

README.md

@@ -56,6 +56,8 @@ If you use this code in another project don't forget to add `cartridge-driver` d
   Determining bucket id on java side to send requests directly on storage.
 * [Thread control](docs/ThreadControl.md)  
   Specifying custom numbers of netty work threads.
+* [Space not found](docs/SpaceNotFound.md)  
+  The problem of getting metadata.
 * [SSL and mTLS usage examples (enterprise edition only)](docs/SslAndMtls.md)  
   Connect to Tarantool instances over an SSL or mTLS channel.
 

docs/SpaceNotFound.md

@@ -0,0 +1,27 @@
+[Main page](../README.md)
+
+# How to set schema and do not get "space not found" error?
+
+## About problem
+If you create spaces only on storages inside a storage role [like this](https://github.com/tarantool/cartridge-java/blob/ba6e8b248b6f448cc9f29e4d660a3d0a2f210ccd/src/test/resources/cartridge/app/roles/api_storage.lua#L12-L220)
+or any other way, and you want to get data using router. You will receive an error message like "space not found".  
+This happens because router does not have information about this space.  
+If you work directly with a storage you won't get this kind of error if spaces was created properly.  
+But if you want to use [CRUD](https://github.com/tarantool/crud) to retrieve data from the router, there are some solutions.  
+
+## Migrations
+We recommend to set the scheme using migrations, they will be applied not only to storages, but also to routers.  
+This way the router will be aware of the current scheme and such errors will not occur.
+Migrations will create spaces on both storages and routers.  
+Tarantool CE supports migrations only since 2.2.x.
+[Tarantool Enterprise Edition](https://www.tarantool.io/ru/product/enterprise/) supports migrations since 1.10.x and 2.2.x.
+More information about migrations [tarantool/migrations](https://github.com/tarantool/migrations).  
+
+## Proxying ddl.get_schema
+If you want to create spaces only in storages, there is another solution.
+Set up proxying ddl.get_schema from storage to routers. You should add this function to router role:
+https://github.com/tarantool/cartridge-java/blob/ba6e8b248b6f448cc9f29e4d660a3d0a2f210ccd/src/test/resources/cartridge/app/roles/api_router.lua#L10-L14
+And make it global.
+https://github.com/tarantool/cartridge-java/blob/ba6e8b248b6f448cc9f29e4d660a3d0a2f210ccd/src/test/resources/cartridge/app/roles/api_router.lua#L228
+Or you can just remove word `local` from line 10. Effect will be the same.
+Now then cartridge-java tries to get schema from router