updating README

README.md

@@ -14,3 +14,45 @@ Stan's home page, with links to everything you'll need to use the Stan Math Libr
 Licensing
 ---------
 The Stan Math Library is licensed under new BSD.
+
+
+Installation
+------------
+The Stan Math Library is a header-only C++ library. To use the Stan Math Library, add the current directory to the source path (in `g++` and `clang++` it is the `-I <math directory>` option) and add this to your source file: `#include <stan/math.hpp>`.
+
+Running Tests
+-------------
+Running tests in the Stan Math Library require these libraries:
+
+- Boost
+- Eigen
+- Google Test
+- CppLint (optional)
+
+If the Stan Math Library has been cloned as part of the Stan library, no configuration is necessary.
+
+If the Stan Math Library is outside of the Stan library, the following variables have to be provided to make in either `make/local` or `~/.config/stan/make.local`:
+
+- `STANAPI_HOME` (the home directory of the Stan library)
+
+or
+
+- `EIGEN`
+- `BOOST`
+- `GTEST`
+- `CPPLINT` (optional)
+
+If you see this message:
+
+```
+------------------------------------------------------------
+make generate-tests -s
+test/prob/generate_tests.cpp:9:10: fatal error: 'boost/algorithm/string.hpp' file not found
+#include <boost/algorithm/string.hpp>
+         ^
+1 error generated.
+make: *** [test/prob/generate_tests] Error 1
+make generate-tests -s failed
+```
+
+the library paths have not been configured correctly.