doc(README): add notes on timestamps for events

The January meetup was shown as being at 4:30PM ET due to the UTC offset
in the front matter being `-04:00` while the current east coast time is
`-05:00`. This corrects that for this event (even though it's over) and
adds a note to the README and the `event-frontmatter.txt` template file
about the correct offsets for Eastern Time, which is likely to be the
most relevant timezone for the community.

The conversion to local timezone is done in JavaScript so it doesn't
really matter what the offset is so long as the overall time is correct
but thinking in east coast time is probably the mostly likely mindset
for contributors (and causes less friction than requiring all times be
specified in UTC).

README.md

@@ -40,7 +40,8 @@ expedite the process.
 #### Details to add an event
 
 Event information is stored in the `_events/` directory. To add a new a event, create a file in
-that folder using a `.html` or `.md` file extension. Start your file with the following content:
+that folder using a `.html` or `.md` file extension. Start your file with the following content
+(or copy the template file `event-frontmatter.txt`):
 
 ```md
 ---
@@ -56,7 +57,8 @@ The first field to add is the title; between the sets of dashes add a like that
 On a new line, add a line that begins with `start-date: ` and then format the start date of the
 event using ISO 8601 format including the event time zone. For example,
 `2023-04-17T22:07:43-04:00`. Then add a line that begins with `end-date: ` and do the same for
-end date/time of the event.
+end date/time of the event. Remember that Eastern Time in the US is `-04:00` during the
+summer (EDT) and `-05:00` during the winter (EST).
 
 Next, add a line that begins with `location: ` and add a human-readable location for where the
 event takes place. This should include the name of the building/business and the city where the

_events/2024-01-maoc-meetup.md

@@ -1,6 +1,6 @@
 ---
-start-date: 2024-01-24T17:30:00-04:00
-end-date: 2024-01-24T19:00:00-04:00
+start-date: 2024-01-24T17:30:00-05:00
+end-date: 2024-01-24T19:00:00-05:00
 title: Mid-Atlantic OSCAL Community Meetup (January 2024)
 location: Solace Outpost (Large Meeting Room)
 map-link: https://goo.gl/maps/Zat8RT1revNvnW9G6

event-frontmatter.txt

@@ -1,4 +1,8 @@
 ---
+# Timestamps should be in RFC 3339 format. The timezone
+# will be converted to the client's local time in JavaScript.
+# US Eastern Time is UTC-04:00 from Mar-Nov and UTC-05:00 from
+# Nov-Mar.
 start-date:
 end-date:
 title: