Add a GitHub issue template for documentation issues

This template automatically adds the [issue: documentation] label.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10051)

.github/ISSUE_TEMPLATE/documentation.md

@@ -0,0 +1,14 @@
+---
+name: Documentation
+labels: 'issue: documentation'
+about: Report an error in (or missing) documentation
+---
+
+<!--
+Thank you for taking the time to report a documentation issue.
+
+Please remember to tell us which OpenSSL version you are using and then
+briefly describe the documentation error and where you encountered it
+(e.g., in which manual page). If you are missing the documentation for a
+certain command or API function, please tell us its name.
+-->