Created Label guide (markdown)

Label-guide.md

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+This is __WHAT WILL BECOME__ a description of what the issue labels mean and how they are used.
+
+## Type labels
+An issue will receive only one of these.  Every issue should get a type eventually, but if it's unclear it's better to wait.
+
+### bug
+Bug reports and bug fix pull requests.
+
+### question
+Design discussions, meta-discussions about the project and support requests not caused by an external bug.
+
+### enhancement
+Feature requests and feature addition pull requests.
+
+## Status
+These may be combined as necessary.
+
+### verified
+The bug has been reproduced by a maintainer, or possibly verified via documentation, and will very likely be fixed.
+
+### waiting for reply
+The maintainer needs more information before being able to continue working on it.  Please always check the [contribution guide](https://github.com/glfw/glfw/blob/master/.github/CONTRIBUTING.md) when creating an issue and add any recommended information.
+
+### cannot reproduce
+No maintainer has been able to reproduce the issue or verify it via documentation.  If you can reproduce it and have the time, please volunteer to help test or develop a fix.
+
+### invalid
+This issue appears to make no sense.
+
+### external
+This bug is caused by something other than GLFW, in a way that GLFW cannot or should not work around.
+
+### wontfix
+This issue is valid but has been rejected.
+
+### duplicate
+This is a duplicate or near duplicate of an existing issue, usually but not always an older one.  Typically an issue is closed when it is marked as a duplicate.
+
+### critical
+This issue is high-impact and must be resolved before the next release.
+
+## GPU manufacturer
+
+### Nvidia, Intel, AMD
+This issue applies to only a single GPU manufacturer. These do not indicate CPU manufacturer.
+
+## Platform
+
+### Linux, Windows, macOS, NetBSD, X11, OpenBSD, Cygwin, Wayland, Mir
+These should be fairly self-explanatory.  Add all that apply.  Issues with none of these are platform independent.
+
+## Area
+
+### Vulkan
+This issue relates to [Vulkan](https://en.wikipedia.org/wiki/Vulkan_(API)) support.
+
+### HDR
+This issue relates to high dynamic range in the sense of deep color and/or wide gamut support.
+
+### Rift
+This issue relates to rendering to an Oculus Rift, usually via LibOVR.
+
+### High-DPI
+This issue relates to support for high-resolution monitors such as Apple's Retina.
+
+### documentation
+This issue relates to the documentation.