html/template: update the documentation of the package

Moved the rationale and workaround from template.Parse()'s
documentation to the package documentation, provided the link
of the issue for more information.

Author: hellozee

src/html/template/doc.go

@@ -73,6 +73,10 @@ functions.
 For these internal escaping functions, if an action pipeline evaluates to
 a nil interface value, it is treated as though it were an empty string.
 
+HTML/CSS/JS comments make the injection context ambiguous, and so correct
+escaping can't be guaranteed. A possible workaround is using a template.HTML variable.
+For more information you can refer to this https://github.com/golang/go/issues/28628
+
 Errors
 
 See the documentation of ErrorCode for details.

src/html/template/template.go

@@ -174,9 +174,7 @@ func (t *Template) DefinedTemplates() string {
 // Named template definitions ({{define ...}} or {{block ...}} statements) in text
 // define additional templates associated with t and are removed from the
 // definition of t itself. Comments in the html format i.e <!-- comment -->
-// are stripped while parsing, this is because they make the injection context
-// ambiguous, and so correct escaping can't be guaranteed. A possible workaround
-// is using a template.HTML variable.
+// are stripped while parsing.
 //
 // Templates can be redefined in successive calls to Parse,
 // before the first use of Execute on t or any associated template.