doc: add function doc for config_overrides_from_env

instrumentation/base/lib/opentelemetry/instrumentation/base.rb

@@ -326,6 +326,18 @@ def enabled_by_env_var?
         ENV[var_name] != 'false'
       end
 
+      # Checks to see if the user has passed any environment variables that set options
+      # for instrumentation. By convention, the environment variable will be the name 
+      # of the instrumentation, uppercased, with '::' replaced by underscores, 
+      # OPENTELEMETRY shortened to OTEL_{LANG}, and _CONFIG_OPTS appended.
+      # For example, the environment variable name for OpenTelemetry::Instrumentation::Faraday
+      # will be OTEL_RUBY_INSTRUMENTATION_FARADAY_CONFIG_OPTS. A value of 'peer_service=new_service;'
+      # will override the options set from ::OpenTelemetry::SDK.configure do |c| ... end for Faraday.
+      #
+      # For an array option, simply separate the values with commas (e.g., option=a,b,c,d).
+      # For a boolean option, set the value to true or false (e.g., option=true).
+      # For integer, string, enum, set the value as a string (e.g., option=string).
+      # Callable options are not allowed to be set through environment variables.
       def config_overrides_from_env
         var_name = name.dup.tap do |n|
           n.upcase!