docs: expand on TODOs in BUILD.gn

build/args/release.gn

@@ -1,6 +1,5 @@
 import("all.gn")
 is_component_build = false
-is_component_ffmpeg = true
 is_official_build = true
 strip_debug_info = true
 
@@ -10,3 +9,9 @@ strip_debug_info = true
 # The initialization of the decoder depends on whether ffmpeg has
 # been built with H.264 support.
 rtc_use_h264 = proprietary_codecs
+
+# By default, Electron builds ffmpeg with proprietary codecs enabled. In order
+# to facilitate users who don't want to ship proprietary codecs in ffmpeg, or
+# who have an LGPL requirement to ship ffmpeg as a dynamically linked library,
+# we build ffmpeg as a shared library.
+is_component_ffmpeg = true