chore: add descriptions for patches (electron#26671)

Author: zcbenz

patches/ReactiveObjC/build_conditionally_import_ext_headers_from_framework_or_from.patch

@@ -4,6 +4,8 @@ Date: Fri, 26 Jun 2020 11:06:12 -0700
 Subject: build: conditionally import EXT headers from framework or from
  relative path
 
+This patch is required for building Squirrel from source code.
+
 diff --git a/ReactiveObjC/NSControl+RACTextSignalSupport.m b/ReactiveObjC/NSControl+RACTextSignalSupport.m
 index 88da38f6e8117bbabdd898c8a1d4bde5e59deda7..483caea62eaaf26d9ad7d267a5c3e9aa44638ce7 100644
 --- a/ReactiveObjC/NSControl+RACTextSignalSupport.m

patches/chromium/feat_allow_embedders_to_add_observers_on_created_hunspell.patch

@@ -4,6 +4,8 @@ Date: Sun, 1 Mar 2020 16:33:55 -0800
 Subject: feat: allow embedders to add observers on created hunspell
  dictionaries
 
+This patch is used by Electron to implement spellchecker events.
+
 diff --git a/chrome/browser/spellchecker/spellcheck_service.cc b/chrome/browser/spellchecker/spellcheck_service.cc
 index 09256573b848bbb248530f77619df47ddbeb8a0e..75b70e375ed1d680cbd2fba1ca73a4e2e5403fb6 100644
 --- a/chrome/browser/spellchecker/spellcheck_service.cc

patches/node/fix_expose_tracing_agent_and_use_tracing_tracingcontroller_instead.patch

@@ -4,6 +4,8 @@ Date: Fri, 26 Oct 2018 15:35:13 +1100
 Subject: fix: expose tracing::Agent and use tracing::TracingController instead
  of v8::TracingController
 
+This API is used by Electron to create Node's tracing controller.
+
 diff --git a/src/api/environment.cc b/src/api/environment.cc
 index 2c4acbc4fa0eca3b7c6d03b997445633646446e7..53b07052e43a09f29f863ee1b2287bdebe7b7a7f 100644
 --- a/src/api/environment.cc