docs, tpl: Fix documentation of UniqueID

See #2861

docs/content/templates/variables.md

@@ -68,7 +68,7 @@ matter, content or derived from file location.
 **.Truncated** A boolean, `true` if the `.Summary` is truncated.  Useful for showing a "Read more..." link only if necessary.  See [Summaries](/content/summaries/) for more details.<br>
 **.Type** The content [type](/content/types/) (e.g. post).<br>
 **.URL** The relative URL for this page. Note that if `URL` is set directly in frontmatter, that URL is returned as-is.<br>
-**.UniqueID** The MD5-checksum of the page's filename<br>
+**.UniqueID** The MD5-checksum of the content file's path<br>
 **.Weight** Assigned weight (in the front matter) to this content, used in sorting.<br>
 **.WordCount** The number of words in the content.<br>
 

source/file.go

@@ -32,13 +32,13 @@ type File struct {
 	section     string // The first directory
 	dir         string // The relative directory Path (minus file name)
 	ext         string // Just the ext (eg txt)
-	uniqueID    string // MD5 of the filename
+	uniqueID    string // MD5 of the file's path
 
 	translationBaseName string // `post` for `post.es.md` (if `Multilingual` is enabled.)
 	lang                string // The language code if `Multilingual` is enabled
 }
 
-// UniqueID is the MD5 hash of the filename and is for most practical applications,
+// UniqueID is the MD5 hash of the file's path and is for most practical applications,
 // Hugo content files being one of them, considered to be unique.
 func (f *File) UniqueID() string {
 	return f.uniqueID