.hgignore: add comment setting policy

R=golang-codereviews, rsc CC=golang-codereviews https://golang.org/cl/44850043
2013-12-20 16:30:01 -08:00 · 2013-12-20 16:30:01 -08:00 · 756628658b
--- a/.hgignore
+++ b/.hgignore
@ -1,2 +1,3 @@
+# Add no patterns to .hgignore except for files generated by the build.
 syntax:glob
 last-change