[issues] Add "Customer request" template (#708)

Author: joshlf

.github/ISSUE_TEMPLATE/customer-request.md

@@ -0,0 +1,17 @@
+---
+name: Customer request
+about: Describe what features you'd like from zerocopy for your project
+title: Features to support <project>
+labels: customer-request
+assignees: ''
+
+---
+
+**What is the name of your project?**
+
+**Please provide a link to your project (GitHub repository, crates.io page, etc).**
+
+**What features would you like from zerocopy?**
+For each feature:
+- Describe why it would be useful to your project, providing any useful context (GitHub links, etc).
+- If there is an existing zerocopy GitHub issue describing this feature, link to it.