Update .gitattributes to force GH linguist to recognize pages (#5663)

.gitattributes

@@ -3,3 +3,8 @@
 # be checked-out as CRLF, and re-converted to LF before check-in.
 # See https://git-scm.com/docs/gitattributes for more information.
 * text=auto
+
+# GitHub linguist ignores markdown files by default, but tldr-pages
+# is mostly markdown, so we explicitly make the pages detectable
+pages*/**/*.md linguist-detectable=true
+pages*/**/*.md linguist-documentation=false