Document uploading a Solr search schema

[lukebakken]

and associating it with an index and bucket type.

From https://github.com/lukebakken/riak-data-loader/blob/master/tweets-idx-setup.sh

curl -XPUT -iH 'Content-Type: application/xml' 'http://localhost:8098/search/schema/tweets-sch' --data-binary @twitter-schema.xml

curl -XPUT -iH 'Content-Type: application/json' http://localhost:8098/search/index/tweets-idx -d '{"schema":"tweets-sch"}'

riak-admin bucket-type create tweets-type '{"props":{"search_index":"tweets-idx"}}'
riak-admin bucket-type activate tweets-type

It should probably go into one or more of these docs:

source/languages/en/riak/ops/advanced/upgrading-search2.md
source/languages/en/riak/dev/using/search.md
source/languages/en/riak/dev/advanced/search-schema.md

[coderoshi]

Snuck into this PR

fb69d68