Create missing_data issue template

For example on the solo results page on the website, in case anything beyond an individual source is missing (e.g. RVs from Author+YY)

.github/ISSUE_TEMPLATE/missing_data

@@ -0,0 +1,18 @@
+---
+name: Missing Data
+about: Report missing data from the database
+title: 'Additional data ingest request from: <publication>'
+labels: data ingestion
+assignees: ''
+
+---
+
+Please provide as much information about what is missing, as possible. 
+
+# Source/survey/catalogue name(s)
+
+# SIMBAD/CDS/Vizier link to data source(s), if available
+
+# What data is missing?
+
+# Reference paper or publically accessible link (e.g. NASA ADS/ArXiV) to the missing publication