chore(doc): fix typo in extra tags

README.md

@@ -435,7 +435,7 @@ When publishing the _release_ image, the Docker template might publish it again
 
 * `$DOCKER_RELEASE_EXTRA_TAGS_PATTERN` supports capturing groups:
     * `v([0-9]+)\.([0-9]+)\.([0-9]+)` has 3 (unnamed) capturing groups, each capturing any number of digits
-    * `v(P<major>[0-9]+)\.(P<minor>[0-9]+)\.(P<patch>[0-9]+)` has 3 **named** capturing groups (_major_, _minor_ and _patch_), each capturing any number of digits
+    * `v(?<major>[0-9]+)\.(?<minor>[0-9]+)\.(?<patch>[0-9]+)` has 3 **named** capturing groups (_major_, _minor_ and _patch_), each capturing any number of digits
 * `$DOCKER_RELEASE_EXTRA_TAGS` supports capturing group references from `$DOCKER_RELEASE_EXTRA_TAGS_PATTERN`: 
     * `\g1` is a reference to capturing group number 1
     * `\g<major>` is a reference to capturing group named _major_