Add metadata to environments.md

I had to link it twice today in discord and the embeds
looks ugly without this :)

Author: naveen521kk

web/docs/environments.md

@@ -1,3 +1,10 @@
+---
+title: Environments
+summary: The differences between the environments is
+    mainly between environment variables, default compilers/linkers, architecture,
+    system libraries used etc.
+---
+
 # Environments
 
 MSYS2 comes with different environments/subsystems and the first thing you have