Minor Documentation and Makefile fixes (#89)

* wrap lines for long lines in README.md so it's easier to read with multiple tabs open (and more consistent with the rest of the file's formatting.

* Add a 'clean' rule to make file so we can do 'make clean build' and know the old artifact is removed first.

GNUmakefile

@@ -5,6 +5,13 @@ PKG_NAME=ns1
 
 default: build
 
+clean:
+	@if [[ -f $(GOPATH)/bin/terraform-provider-ns1 ]]; then \
+		rm $(GOPATH)/bin/terraform-provider-ns1; \
+	else \
+		echo "nothing to clean."; \
+	fi
+
 build: fmtcheck
 	go install
 

README.md

@@ -347,9 +347,12 @@ For each of those resources, these parameters are available at the top level of
 Developing The Provider
 ---------------------------
 
-If you wish to work on the provider, you'll first need [Go](http://www.golang.org) installed on your machine (version 1.11+ is *required*). You'll also need to correctly setup a [GOPATH](http://golang.org/doc/code.html#GOPATH), as well as adding `$GOPATH/bin` to your `$PATH`.
+If you wish to work on the provider, you'll first need [Go](http://www.golang.org) installed on your machine 
+(version 1.11+ is *required*). You'll also need to correctly setup a [GOPATH](http://golang.org/doc/code.html#GOPATH),
+as well as adding `$GOPATH/bin` to your `$PATH`.
 
-To compile the provider, run `make build`. This will build the provider and put the provider binary in the `$GOPATH/bin` directory.
+To compile the provider, run `make build`. This will build the provider and put the provider binary in 
+the `$GOPATH/bin` directory.
 
 ```sh
 $ make bin