Merge pull request #2 from OHDSI/master

updating with the OHDSI master
Update README.md
Update OMOPv4_to_PCORnetv1_ETL_Description.md
Update OMOPv4_to_PCORnetv1_ETL_Description.md
Update to Vital query 

removed the condition on bp_position in the last clause 
reason: the value for the bp_position is never null, hence this condition would still generate records with null values in all observation-related  columns (except bp_position)
adding pdf version of the doc
Update README.md
Merge pull request #9 from writetoritu/master

Modified "Vitals" query and minor changes to documentation