Update Makefile & build instructions

Makefile

@@ -1,7 +1,20 @@
+.PHONY: build
+build: ## Build debug target for development.
+	rustup default nightly-2019-10-05
+	pip install -r requirements.txt
+	python setup.py build
+
 .PHONY: help
-help: ## Print help.
-	@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}' \
-	$(MAKEFILE_LIST) | sort
+help: ## Print help information.
+	@awk 'BEGIN { \
+        FS = ":.*?## " \
+    } /^[a-zA-Z_-]+:.*?## / { \
+        printf "\033[36m%-30s\033[0m %s\n", $$1, $$2 \
+    }' $(MAKEFILE_LIST)
+
+.PHONY: install
+install: ## Install local target.
+	pip install .
 
 .PHONY: mac
 mac: ## Build wheel distributions for macOS.

README.md

@@ -39,16 +39,30 @@ If that fails, install [rustup](https://rustup.rs) and then run:
     $ pip install -U setuptools-rust
     $ pip install -U autopy
 
-Another option is to compile from the latest source on the GitHub repository:
+Another option is to build from the latest source on the GitHub repository:
 
     $ git clone git://github.com/autopilot-rs/autopy-rs.git
     $ cd autopy
-    $ rustup default nightly-2019-10-05
-    $ pip install -r requirements.txt
-    $ python setup.py build
-    # python setup.py install
+    $ make
+    $ make install
+
+**Note**: AutoPy currently requires the `2019-10-05` Rust nightly in order to
+build from source. This is to maintain compatibility with an older version of
+PyO3, as the latest version has dropped Python 2 support. Python 2 support will
+likely be dropped from AutoPy as well sometime later this year, depending on
+how necessary it is to upgrade to a more recent version of PyO3 or Rust. In the
+meantime, it may be necessary to install the required nightly via the following
+when building locally:
+
+```
+rustup install nightly 2019-10-05 --force
+```
+
+This is due to rustup complaining that it doesn't include certain components
+such as `rustfmt`.
 
-Additional instructions for installing from source on Windows are available [here](https://github.com/autopilot-rs/autopy/blob/master/scripts/windows-setup.md).
+Additional instructions for installing from source on Windows are available
+[here](https://github.com/autopilot-rs/autopy/blob/master/scripts/windows-setup.md).
 
 ### Hello World