Adds inline make documentation and 'help' command. (mattermost#394)

Makefile

@@ -1,14 +1,14 @@
-.PHONY: build test run clean stop check-style run-unit emojis
+.PHONY: build test run clean stop check-style run-unit emojis help
 
 BUILD_SERVER_DIR = ../mattermost-server
 EMOJI_TOOLS_DIR = ./build/emoji
 
-check-style: .yarninstall
+check-style: .yarninstall ## Checks JS file for ESLint confirmity
  @echo Checking for style guide compliance
 
  yarn run check
 
-test: .yarninstall
+test: .yarninstall ## Runs tests
  @echo Running jest unit/component testing
 
  yarn run test
@@ -21,7 +21,7 @@ test: .yarninstall
 
  touch $@
 
-package: build
+package: build ## Packages app
  @echo Packaging webapp
 
  mkdir tmp
@@ -30,25 +30,24 @@ package: build
  mv tmp/client dist
  rmdir tmp
 
-
-build: .yarninstall
+build: .yarninstall ## Builds the app
  @echo Building mattermost Webapp
 
  rm -rf dist
 
  yarn run build
 
-run: .yarninstall
+run: .yarninstall ## Runs app
  @echo Running mattermost Webapp for development
 
  yarn run run &
 
-run-fullmap: .yarninstall
+run-fullmap: .yarninstall ## Runs the app with the JS mapped to source (good for debugger)
  @echo FULL SOURCE MAP Running mattermost Webapp for development FULL SOURCE MAP
 
  yarn run run-fullmap &
 
-stop:
+stop: ## Stops webpack
  @echo Stopping changes watching
 
 ifeq ($(OS),Windows_NT)
@@ -60,7 +59,7 @@ else
  done
 endif
 
-clean:
+clean: ## Clears cached; deletes node_modules and dist directories
  @echo Cleaning Webapp
 
  yarn cache clean
@@ -69,7 +68,11 @@ clean:
  rm -rf node_modules
  rm -f .yarninstall
 
-emojis:
+emojis: ## Creates emoji JSX file and extracts emoji images from the system font
  gem install bundler
  bundle install --gemfile=$(EMOJI_TOOLS_DIR)/Gemfile
  BUNDLE_GEMFILE=$(EMOJI_TOOLS_DIR)/Gemfile bundle exec $(EMOJI_TOOLS_DIR)/make-emojis
+
+## Help documentatin à la https://marmelab.com/blog/2016/02/29/auto-documented-makefile.html
+help:
+ @grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'