create issue templates (#21)

.github/ISSUE_TEMPLATE/01-general.md

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+---
+name: General
+about: General issue or request
+---

.github/ISSUE_TEMPLATE/02-wmo-amendment-proposal.md

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+---
+name: WMO amendment proposal
+about: Proposals for amendments to this specification
+---
+
+> Note: sections marked with * are required.
+
+# Overview of proposal*
+_(Brief description of the amendment(s) requested. Include as much relevant information as possible, such as rationale, purpose, and implementation plans.)_
+
+# Amendment details*
+_(The exact changes proposed. Enter TBD if the details are unknown. This content may evolve as decisions are finalized.)_
+
+# Requestor(s)*
+_(Name of individuals, groups, or organizations that are requesting the amendment. Include relevant affiliations and GitHub user names, as applicable.)_
+
+# Consulations
+_(Individuals, groups,or organizations that are consulted. Also cite publications or other documents that as references.)_
+
+# Comments