docs: add changelog to launcher (GoogleChrome/lighthouse#2987)

changelog.md

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+## 0.5.0 (Mon, 14 Aug 2017)
+* `494f9911` clarify priority of chromePath options
+* `1c11021a` add support for finding Chromium on Linux (#2950)
+* `391e2043` Publish type definitions instead of source TypeScript files (#2898)
+* `de408ad3` readme: update example using deprecated `LIGHTHOUSE_CHROMIUM_PATH` (#2929)
+* `8bc6d18e` add license file to launcher package. (#2849)
+
+## 0.4.0 (Tue, 1 Aug 2017)
+* `37fd38ce` pass --enable-extensions on from manual-chrome-launcher (#2735)
+* `c942d17e` support enabling extension loading (#2650)
+
+## 0.3.2 (Wed, 19 Jul 2017)
+* `112c2c7f` Fix chrome finder on linux/osx when process.env isn't populated (#2687)
+* `5728695f` Added CHROME_PATH to readme (#2694)
+* `fedc76a3` test: fix clang-format error (#2691)
+* `a6bbcaba` nuke 'as string'
+* `41df647f` cli: remove --select-chrome,--skip-autolaunch. Support CHROME_PATH env  (#2659)
+* `8c9724e2` fix launcher w/ arbitrary flags (#2670)
+* `9c0c0788` Expose LHR to modules consuming cli/run.ts (#2654)
+* `6df6b0e2` support custom port via chrome-debug binary (#2644)
+* `3f143b19` log the specific chrome spawn command.
+
+## 0.3.1 (Wed, 5 Jul 2017)
+* `ef081063` upgrade rimraf to latest (#2641)
+
+## 0.3.0 (Fri, 30 Jun 2017)
+* `edbb40d9` fix(driver): move performance observer registration to setupDriver (#2611)