docs: add docs about timestamps

README.org

@@ -41,6 +41,18 @@ The link will reference the current Org Mode paragraph. If you want to reference
 Run =M-x org-journal-tags-link-get-region-at-point= to select the referenced region of the buffer.
 
 To add a tag to the entire section, run =M-x org-journal-tags-prop-set=, which will create or update the =Tags= property in the property drawer of the current time section. This command features a notmuch-like UI, i.e. completing read for multiple entries, where =+<tag>= adds a tag and =-<tag>= deletes a tag.
+** Adding timestamps
+In addition to tags, the package also aggregates inline timestamps, i.e. timestamps that are left in the text like this:
+
+#+begin_example
+This is a text. This is a text with <2022-04-07 Thu> a timestamp. This is a text again.
+#+end_example
+
+A timestamp will reference just the current paragraph.
+
+Other forms of timestamps (=SCHEDULED=, =DEADLINE=, etc.) are not supported at the moment, because this functionality is implemented well enough by [[https://orgmode.org/manual/Agenda-Views.html][org-agenda]].
+
+The envisioned use case for this functionality to leave references for the future to be seen at a particular date.
 
 ** Database
 The package stores tags and references to these tags in a database.
@@ -71,6 +83,9 @@ The options are as follows:
 - *Exclude tags* filters the references so that each reference didn't have any of these tags.
 - *Include children* includes child tags to the previous two lists.
 - *Start date* and *End date* filter the references by date.
+- *Filter timestamps* filters the references so that they include a timestamp.
+- *Timestamp start date* and *Timestamp end date* filter
+  timestamps by their date.
 - *Regex* filter the references by a regular expression. It can be a string or [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Rx-Notation.html][rx]] expression (it just has to start with =(rx= in this case).
 - *Narrow to regex* makes it so that each reference had only paragraphs that have a regex match.
 - *Sort* sorts the result in ascending order. It's descending by default.

org-journal-tags.el

@@ -179,7 +179,7 @@ detail."
   :type 'function
   :group 'org-journal-tags)
 
-(defcustom org-journal-tags-timestamps '((:start . 0) (:end . 2678400))
+(defcustom org-journal-tags-timestamps '((:start . 0) (:end . 1209600))
   "Whether and how to display timestamps in the status buffer.
 
 If nil, do not display.
@@ -194,8 +194,8 @@ If non-nil, this has to a an alist with the following properties:
 - `:end': End of the range for which to filter timestamps.  The rules
   are the same as for `:start'.
 
-E.g. the default value of ((:start . 0) (:end . 2678400)) filters
-timestamps between today and +31 days from today."
+E.g. the default value of ((:start . 0) (:end . 1209600)) filters
+timestamps between today and +14 days from today."
   :group 'org-journal-tags
   :type '(choice (const :tag "Do not display" nil)
                  (repeat :tag "Display parameters"
@@ -2287,6 +2287,10 @@ The options are as follows:
   didn't have any of these tags.
 - \"Include children\" includes child tags to the previous two lists.
 - \"Start date\" and \"End date*\" filter the references by date.
+- \"Filter timestamps\" filters the references so that they include a
+  timestamp.
+- \"Timestamp start date\" and \"Timestamp end date\" filter
+  timestamps by their date.
 - \"Regex\" filter the references by a regular expression.  It can be a
   string or `rx' expression (it just has to start with =(rx= in this
   case).