update readme

Adds install instructions for using modules, as well as adding the
new google group link.  Fixes magefile#200.

README.md

@@ -5,29 +5,36 @@
 
 ## About 
 
-Mage is a make/rake-like build tool using Go.  You write plain-old go functions,
+Mage is a make-like build tool using Go.  You write plain-old go functions,
 and Mage automatically uses them as Makefile-like runnable targets.
 
 ## Installation
 
 Mage has no dependencies outside the Go standard library, and builds with Go 1.7
 and above (possibly even lower versions, but they're not regularly tested). 
 
-Install mage by running 
+**Using GOPATH**
 
 ```
 go get -u -d github.com/magefile/mage
 cd $GOPATH/src/github.com/magefile/mage
 go run bootstrap.go
 ```
 
-This will download the code into your GOPATH, and then run the bootstrap script
-to build mage with version infomation embedded in it.  A normal `go get`
-(without -d) will build the binary correctly, but no version info will be
-embedded.  If you've done this, no worries, just go to
-$GOPATH/src/github.com/magefile/mage and run `mage install` or `go run
-bootstrap.go` and a new binary will be created with the correct version
-information.
+**Using Go Modules**
+
+```
+git clone https://github.com:magefile/mage
+cd mage
+go run bootstrap.go
+```
+
+This will download the code and then run the bootstrap script to build mage with
+version infomation embedded in it.  A normal `go get` (without -d) or `go
+install` will build the binary correctly, but no version info will be embedded.
+If you've done this, no worries, just go to `$GOPATH/src/github.com/magefile/mage`
+and run `mage install` or `go run bootstrap.go` and a new binary will be created
+with the correct version information.
 
 The mage binary will be created in your $GOPATH/bin directory.
 
@@ -40,7 +47,9 @@ You may also install a binary release from our
 
 ## Discussion
 
-Join the `#mage` channel on [gophers slack](https://gophers.slack.com/messages/general/) for discussion of usage, development, etc.
+Join the `#mage` channel on [gophers slack](https://gophers.slack.com/messages/general/) 
+or post on the [magefile google group](https://groups.google.com/forum/#!forum/magefile) 
+for discussion of usage, development, etc.
 
 # Documentation
 
@@ -50,15 +59,16 @@ see [godoc.org/github.com/magefile/mage/mage](https://godoc.org/github.com/magef
 
 # Why?
 
-Makefiles are hard to read and hard to write.  Mostly because makefiles are essentially fancy bash scripts with significant white space and additional make-related syntax.
-
-Mage lets you have multiple magefiles, name your magefiles whatever you
-want, and they're easy to customize for multiple operating systems.  Mage has no
-dependencies (aside from go) and runs just fine on all major operating systems, whereas make generally uses bash which is not well supported on Windows.
-Go is superior to bash for any non-trivial task involving branching, looping, anything that's not just straight line execution of commands.  And if your project is written in Go, why introduce another
-language as idiosyncratic as bash?  Why not use the language your contributors
-are already comfortable with?
+Makefiles are hard to read and hard to write.  Mostly because makefiles are
+essentially fancy bash scripts with significant white space and additional
+make-related syntax.
 
-# TODO
+Mage lets you have multiple magefiles, name your magefiles whatever you want,
+and they're easy to customize for multiple operating systems.  Mage has no
+dependencies (aside from go) and runs just fine on all major operating systems,
+whereas make generally uses bash which is not well supported on Windows. Go is
+superior to bash for any non-trivial task involving branching, looping, anything
+that's not just straight line execution of commands.  And if your project is
+written in Go, why introduce another language as idiosyncratic as bash?  Why not
+use the language your contributors are already comfortable with?
 
-* File conversion tasks