added README.md to openMP example
added README.md to openMP example

javierip/parallel-code-examples,javierip/parallel-code-examples,javierip/parallel-processing-teaching-toolkit,javierip/parallel-processing-teaching-toolkit,javierip/parallel-code-examples,javierip/parallel-code-examples,javierip/parallel-processing-teaching-toolkit,javierip/parallel-processing-teaching-toolkit,javierip/parallel-processing-teaching-toolkit,javierip/parallel-processing-teaching-toolkit,javierip/parallel-code-examples,javierip/parallel-code-examples