Add pkgconfig to brew install instructions and add vendor via the official dep tool

Gopkg.toml

@@ -0,0 +1,71 @@
+
+## Gopkg.toml example (these lines may be deleted)
+
+## "metadata" defines metadata about the project that could be used by other independent
+## systems. The metadata defined here will be ignored by dep.
+# [metadata]
+# key1 = "value that convey data to other systems"
+# system1-data = "value that is used by a system"
+# system2-data = "value that is used by another system"
+
+## "required" lists a set of packages (not projects) that must be included in
+## Gopkg.lock. This list is merged with the set of packages imported by the current
+## project. Use it when your project needs a package it doesn't explicitly import -
+## including "main" packages.
+# required = ["github.com/user/thing/cmd/thing"]
+
+## "ignored" lists a set of packages (not projects) that are ignored when
+## dep statically analyzes source code. Ignored packages can be in this project,
+## or in a dependency.
+# ignored = ["github.com/user/project/badpkg"]
+
+## Constraints are rules for how directly imported projects
+## may be incorporated into the depgraph. They are respected by
+## dep whether coming from the Gopkg.toml of the current project or a dependency.
+# [[constraint]]
+## Required: the root import path of the project being constrained.
+# name = "github.com/user/project"
+#
+## Recommended: the version constraint to enforce for the project.
+## Only one of "branch", "version" or "revision" can be specified.
+# version = "1.0.0"
+# branch = "master"
+# revision = "abc123"
+#
+## Optional: an alternate location (URL or import path) for the project's source.
+# source = "https://github.com/myfork/package.git"
+#
+## "metadata" defines metadata about the dependency or override that could be used
+## by other independent systems. The metadata defined here will be ignored by dep.
+# [metadata]
+# key1 = "value that convey data to other systems"
+# system1-data = "value that is used by a system"
+# system2-data = "value that is used by another system"
+
+## Overrides have the same structure as [[constraint]], but supersede all
+## [[constraint]] declarations from all projects. Only [[override]] from
+## the current project's are applied.
+##
+## Overrides are a sledgehammer. Use them only as a last resort.
+# [[override]]
+## Required: the root import path of the project being constrained.
+# name = "github.com/user/project"
+#
+## Optional: specifying a version constraint override will cause all other
+## constraints on this project to be ignored; only the overridden constraint
+## need be satisfied.
+## Again, only one of "branch", "version" or "revision" can be specified.
+# version = "1.0.0"
+# branch = "master"
+# revision = "abc123"
+#
+## Optional: specifying an alternate source location as an override will
+## enforce that the alternate location is used for that project, regardless of
+## what source location any dependent projects specify.
+# source = "https://github.com/myfork/package.git"
+
+
+
+[[constraint]]
+  branch = "li/make-surface-implement-image"
+  name = "github.com/veandco/go-sdl2"

README.md

@@ -7,7 +7,7 @@ This is a simple cat game written in Go and SDL, inspired by [flappy](https://gi
 It's been only tested on MacOS, and requires the [SDL](https://www.libsdl.org) library and Go bindings:
 
 ```
-brew install sdl2 sdl2_image sdl2_mixer sdl2_ttf
+brew install sdl2 sdl2_image sdl2_mixer sdl2_ttf pkgconfig
 go get github.com/fiorix/cat-o-licious
 ```