Added entry for Solr for newbies (#5247)

* Added entry for Solr for newbies

* Grouped Solr and ElasticSearch books into Search Engines category as suggested by davorpa

Author: hectorcorrea

books/free-programming-books.md

@@ -41,7 +41,6 @@
 * [Delphi / Pascal](#delphi--pascal)
 * [DTrace](#dtrace)
 * [Eiffel](#eiffel)
-* [Elasticsearch](#elasticsearch)
 * [Elixir](#elixir)
   * [Ecto](#ecto)
   * [Phoenix](#phoenix)
@@ -141,6 +140,7 @@
   * [Programming Paradigms](#programming-paradigms)
   * [Regular Expressions](#regular-expressions)
   * [Reverse Engineering](#reverse-engineering)
+  * [Search Engines](#search-engines)
   * [Security](#security)
   * [Software Architecture](#software-architecture)
   * [Standards](#standards)
@@ -857,6 +857,13 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Reverse Engineering for Beginners](http://beginners.re) - Dennis Yurichev (PDF)
 
 
+#### Search Engines
+
+* [Elasticsearch: The Definitive Guide](https://www.elastic.co/guide/en/elasticsearch/guide/current/index.html) ([fork it on GH](https://github.com/elastic/elasticsearch-definitive-guide))
+* [Exploring Elasticsearch](http://exploringelasticsearch.com)
+* [Solr for newbies workshop (2019)](https://github.com/hectorcorrea/solr-for-newbies) - Hector Correa ([PDF](https://github.com/hectorcorrea/solr-for-newbies/blob/master/tutorial.pdf))
+
+
 #### Security
 
 * [A Graduate Course in Applied Cryptography](http://toc.cryptobook.us)
@@ -1342,12 +1349,6 @@ Kerridge (PDF) (email address *requested*, not required)
 * [IllumOS Dynamic Tracing Guide](http://dtrace.org/guide/preface.html)
 
 
-### Elasticsearch
-
-* [Elasticsearch: The Definitive Guide](https://www.elastic.co/guide/en/elasticsearch/guide/current/index.html) ([fork it on GH](https://github.com/elastic/elasticsearch-definitive-guide))
-* [Exploring Elasticsearch](http://exploringelasticsearch.com)
-
-
 ### Eiffel
 
 * [A Functional Pattern System for Object-Oriented Design](http://homepages.mcs.vuw.ac.nz/~tk/fps/fps-sans-escher.pdf) - Thomas Kuhne (PDF)