feat: add docs

Signed-off-by: Aleksei Muratov <[email protected]>

docs/reference/flag-definitions.md

@@ -184,6 +184,9 @@ For example, when accessing flagd via HTTP, the POST body may look like this:
 
 The evaluation context can be accessed in targeting rules using the `var` operation followed by the evaluation context property name.
 
+The evaluation context can be appended by arbitrary key value pairs
+via the `-X` command line flag.
+
 | Description                                                    | Example                                              |
 | -------------------------------------------------------------- | ---------------------------------------------------- |
 | Retrieve property from the evaluation context                  | `#!json { "var": "email" }`                          |

docs/reference/flagd-cli/flagd_start.md

@@ -11,6 +11,7 @@ flagd start [flags]
 ### Options
 
 ```
+  -X, --context-value stringToString    add arbitrary key value pairs to the flag value evaluation context (default [])
   -C, --cors-origin strings             CORS allowed origins, * will allow all origins
   -h, --help                            help for start
   -z, --log-format string               Set the logging format, e.g. console or json (default "console")

flagd/cmd/start.go

@@ -79,7 +79,7 @@ func init() {
 	flags.StringP(otelCAPathFlagName, "A", "", "tls certificate authority path to use with OpenTelemetry collector")
 	flags.DurationP(otelReloadIntervalFlagName, "I", time.Hour, "how long between reloading the otel tls certificate "+
 		"from disk")
-	flags.StringToStringP(contextValueFlagName, "kv", map[string]string{}, "add arbitrary key value pairs "+
+	flags.StringToStringP(contextValueFlagName, "X", map[string]string{}, "add arbitrary key value pairs "+
 		"to the flag value evaluation context")
 
 	_ = viper.BindPFlag(corsFlagName, flags.Lookup(corsFlagName))