Pretend markdown is a real language

RealOrangeOne · RealOrangeOne · commit e404f2449b80 · 2023-07-15T14:13:58.000+01:00
This makes GitHub detect it, and show it in the language metrics
diff --git a/.gitattributes b/.gitattributes
@@ -0,0 +1 @@
+*.md linguist-detectable=true
