Update docs to include mute time sections

Signed-off-by: Ben Ridley <benridley29@gmail.com>

docs/configuration.md

@@ -113,6 +113,10 @@ receivers:
 # A list of inhibition rules.
 inhibit_rules:
   [ - <inhibit_rule> ... ]
+
+# A list of mute time intervals for muting routes
+mute_time_intervals:
+  [ - <mute_time_interval> ... ]
 ```
 
 ## `<route>`
@@ -168,6 +172,12 @@ match_re:
 # been sent successfully for an alert. (Usually ~3h or more).
 [ repeat_interval: <duration> | default = 4h ]
 
+# Times when the route should be muted. These must match a name of a
+# mute time interval defined in the mute_time_intervals section. 
+# Additionally, the root node cannot have any mute times.
+mute_times:
+  [ - <string> ...]
+
 # Zero or more child routes.
 routes:
   [ - <route> ... ]
@@ -202,6 +212,62 @@ route:
       team: frontend
 ```
 
+## `<mute_time_interval>`
+
+A `mute_time_interval` specifies a named interval of time that may be referenced
+in the routing tree to mute particular routes for particular times of the day.
+
+```yaml
+name: <string>
+time_intervals:
+  [ - <time_interval> ... ]
+
+```
+## `<time_interval>`
+A `time_interval` contains the actual definition for an interval of time. The syntax
+supports the following fields:
+
+```yaml
+- times:
+  [ - <time_range> ...]
+  weekdays:
+  [ - <weekday_range> ...]
+  days_of_month:
+  [ - <days_of_month_range> ...]
+  months:
+  [ - <month_range> ...]
+  years:
+  [ - <year_range> ...]
+```
+
+All these fields are optional and if left unspecified allow any value to match the interval.
+Some fields support ranges and negative indices, and are detailed below:
+
+`times`: A list of time-ranges. They are inclusive of the starting time and exclusive
+of the ending time to make it easy to represent times that start/end on hour boundaries.
+For example, start_time: '17:00' and end_time: '24:00' will begin at 17:00 and finish
+immediately after 23:59. They are specified like so:
+
+        times:
+        - start_time: HH:MM
+          end_time: HH:MM
+
+`weekdays`: A list of days of the week, where the week begins on Sunday and ends on Saturday.
+Days should be specified by name (e.g. ‘Sunday’). For convenience, ranges are also accepted
+of the form <start_day>:<end_day> and are inclusive on both ends. For example:
+`[‘monday:wednesday','saturday', 'sunday']`
+
+`days_of_month`: A list of numerical days in the month. Days begin at 1.
+Negative values are also accepted which begin at the end of the month,
+e.g. -1 during January would represent January 31. For example: `['1:5', '-3:-1']`.
+Extending past the start or end of the month will cause it to be clamped. E.g. specifying
+`['1:31']` during February will clamp the actual end date to 28 or 29 depending on leap years. 
+
+`months`: A list of calendar months identified by a case-insentive name (e.g. ‘January’) or by number,
+where January = 1. Ranges are also accepted. For example, `['1:3', 'may:august', 'december']`
+
+`years`: A numerical list of years. Ranges are accepted. For example, `['2020:2022', '2030']`
+
 ## `<inhibit_rule>`
 
 An inhibition rule mutes an alert (target) matching a set of matchers