Update pojo-overview.markdown

I linked out JavaBean to Oracle docs and fixed a grammar error. 

Does the emphasis (replaced by link) have a meaning for our docs? Like go to a glossary?

Also, "follow rules similar to" is requires some, if not deep, knowledge of these technologies give context to the implication. Strict JavaBean compliance probably is sufficient.
Merge pull request #148 from jasonnerothin/patch-2

Update pojo-overview.markdown