mark copy/rename as experimental in the docs

doc/hg.1.txt

@@ -188,6 +188,10 b' copy <source ...> <dest>::'
 
     This command takes effect in the next commit.
 
+    NOTE: This command should be treated as experimental. While it
+    should properly record copied files, this information is not yet
+    fully used by merge, nor fully reported by log.
+
     Options:
     -A, --after           record a copy that has already occurred
     -I, --include <pat>   include names matching the given patterns
@@ -476,6 +480,10 b' rename <source ...> <dest>::'
 
     This command takes effect in the next commit.
 
+    NOTE: This command should be treated as experimental. While it
+    should properly record rename files, this information is not yet
+    fully used by merge, nor fully reported by log.
+
     Options:
     -A, --after        record a rename that has already occurred
     -f, --force        forcibly copy over an existing managed file