Add Get UTC Offset For Different Time Zones as a Ruby TIL

ruby/get-utc-offset-for-different-time-zones.md

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+# Get UTC Offset For Different Time Zones
+
+The [IANA Time Zone Database](https://www.iana.org/time-zones) uses identifiers
+like `America/Chicago`, `Asia/Hong_Kong`, `Africa/Nairobi`, etc. as specifiers
+for notable locations with time zone information.
+
+> Most timezones correspond to a notable location and the database records all
+> known clock transitions for that location; some timezones correspond instead
+> to a fixed UTC offset.
+—[Theory and pragmatics of the tz code and data](https://data.iana.org/time-zones/theory.html)
+
+These identifiers can be used to look up time zone details with the [`tzinfo`
+gem](https://github.com/tzinfo/tzinfo).
+
+Here is an example of passing one to the `#get` method and then getting the UTC
+offset in seconds.
+
+```ruby
+> require 'tzinfo'
+
+> mountain = TZInfo::Timezone.get('America/Denver')
+=> #<TZInfo::DataTimezone: America/Denver>
+> mountain.utc_offset
+=> -21600
+```
+
+We can even get the base UTC offset that doesn't account for DST:
+
+```ruby
+> moutain.base_utc_offset
+=> -25200
+```
+
+Notice, this is the same as the standard offset for a time zone like Phoenix
+that doesn't observe DST.
+
+```ruby
+> phoenix = TZInfo::Timezone.get('America/Phoenix')
+=> #<TZInfo::DataTimezone: America/Phoenix>
+> phoenix.utc_offset
+=> -25200
+```