README: style updates (#3337)

Improved some stylistic issues.

* Updated Travis CI reference to CircleCI.
* Switched to CircleCI "shield" style badge to fit in better with the other badges.

README.md

@@ -41,19 +41,19 @@ Highlights for developers
 --------------------------
 
 * frontend written in Lua scripting language
-  * running on multi-platform with only one code-base maintained
-  * developing koreader in any editor without compilation
-  * high runtime efficiency by LuaJIT acceleration
+  * multi-platform support through a single code-base
+  * you can help develop KOReader in any editor without compilation
+  * high runtime efficiency through LuaJIT acceleration
   * light-weight self-contained widget toolkit with small memory footprint
   * extensible with plugin system
 * interfaced backends for documents parsing and rendering
   * high quality document backend libraries like MuPDF, DjvuLibre and CREngine
   * interacting with frontend via LuaJIT FFI for best performence
 * in active development
-  * contributed by developers around the world
-  * continuous integration with Travis CI
-  * with unit tests, static analysis and code coverage test
-  * automatic release of nightly builds
+  * with contributions from developers around the world
+  * continuous integration with CircleCI
+  * with unit tests (busted), static code analysis (luacheck) and code coverage test (luacov/coveralls)
+  * automated nightly builds available at http://build.koreader.rocks/download/nightly/
 * free as in free speech
   * licensed under Affero GPL v3
   * all dependencies are free software
@@ -294,7 +294,7 @@ http://ccache.samba.org
 
 [base-readme]:https://github.com/koreader/koreader-base/blob/master/README.md
 [nb-script]:https://gitlab.com/koreader/nightly-builds/blob/master/build_release.sh
-[circleci-badge]:https://circleci.com/gh/koreader/koreader.svg?style=svg
+[circleci-badge]:https://circleci.com/gh/koreader/koreader.svg?style=shield
 [circleci-link]:https://circleci.com/gh/koreader/koreader
 [circleci-conf]:https://github.com/koreader/koreader-base/blob/master/.circleci/config.yml
 [linux-vm]:http://www.howtogeek.com/howto/11287/how-to-run-ubuntu-in-windows-7-with-vmware-player/