Add time to completion.timestamp_format and fix docs

doc/changelog.asciidoc

@@ -42,6 +42,7 @@ Changed
   restore closed windows (rather than tabs). This is bound to `U` by default.
 - When `:undo` is used with a count, it now reopens the count-th to last tab
   instead of the last one.
+- The default `completion.timestamp_format` now also shows the time.
 
 Added
 ~~~~~

doc/help/settings.asciidoc

@@ -1833,11 +1833,11 @@ Default: +pass:[false]+
 [[completion.timestamp_format]]
 === completion.timestamp_format
 Format of timestamps (e.g. for the history completion).
-See https://sqlite.org/lang_datefunc.html for allowed substitutions.
+See https://sqlite.org/lang_datefunc.html and https://docs.python.org/3/library/datetime.html#strftime-strptime-behavior for allowed substitutions, qutebrowser uses both sqlite and Python to format its timestamps.
 
 Type: <<types,String>>
 
-Default: +pass:[%Y-%m-%d]+
+Default: +pass:[%Y-%m-%d %H:%M]+
 
 [[completion.use_best_match]]
 === completion.use_best_match

qutebrowser/config/configdata.yml

@@ -996,11 +996,14 @@ completion.timestamp_format:
   type:
     name: String
     none_ok: true
-  default: '%Y-%m-%d'
+  default: '%Y-%m-%d %H:%M'
   desc: >-
     Format of timestamps (e.g. for the history completion).
 
-    See https://sqlite.org/lang_datefunc.html for allowed substitutions.
+    See https://sqlite.org/lang_datefunc.html and
+    https://docs.python.org/3/library/datetime.html#strftime-strptime-behavior
+    for allowed substitutions, qutebrowser uses both sqlite and Python to
+    format its timestamps.
 
 completion.web_history.exclude:
   type: