Update enhancement.md

Update bug.yaml

Add a basic CONTRIBUTING.md

Issue templates

Provide basic instructions in-repository for contributing to Second
Life.

following promotion of DRTVWR-596

SL-20611 Followup -- fix for depth based atmospheric mask making atmospherics effect sun/moon/clouds

following promotion of DRTVWR-587

Fix for semi-transparent HUDs rendering opaque

and fixed diffuse alpha

This commit fixes a bug introduced with commit 6472b75b
where the fullbrightF.glsl shader fails to set color.a to final_alpha for HUDs.

SL-20611 Brute force fix for water haze -- paid for by cycles saved by not drawing water twice, but needs a better long term solution.

SL-20611 Followup -- fix for artifacts on water surface from GPUs that don't like to read from a depth buffer that is bound for writing

BUG-234706 Fix unstable performance on nvidia systems by always enabling Threaded Optimization via driver application profile (#564)