runtime/pprof: document that profile names should not contain spaces.

Change-Id: I967d897e812bee63b32bc2a7dcf453861b89b7e3
Reviewed-on: https://go-review.googlesource.com/36533Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/pprof/pprof.go

@@ -185,6 +185,8 @@ func unlockProfiles() {
 // If a profile with that name already exists, NewProfile panics.
 // The convention is to use a 'import/path.' prefix to create
 // separate name spaces for each package.
+// For compatibility with various tools that read pprof data,
+// profile names should not contain spaces.
 func NewProfile(name string) *Profile {
 	lockProfiles()
 	defer unlockProfiles()