Add README.md with reference examples and build instructions (#10)

* Finalize README.md

* Fix capitalization

* Update README.md

* Update README.md

* Update build instructions

* Follow formatting of other library README's

* Address PR comments

* Update README formatting

* Update coreJSON description

* Address PR comment

README.md

@@ -0,0 +1,94 @@
+## coreJSON Library
+
+A parser strictly enforcing the ECMA-404 JSON standard, suitable for microcontrollers
+
+## Reference example
+
+```c
+#include <stdio.h>
+#include "core_json.h"
+
+int main()
+{
+    // Variables used in this example.
+    JSONStatus_t result;
+    char buffer[] = "{\"foo\":\"abc\",\"bar\":{\"foo\":\"xyz\"}}";
+    size_t bufferLength = sizeof( buffer ) - 1;
+    char queryKey[] = "bar.foo";
+    size_t queryKeyLength = sizeof( queryKey ) - 1;
+    char * value;
+    size_t valueLength;
+
+    // Calling JSON_Validate() is not necessary if the document is guaranteed to be valid.
+    result = JSON_Validate( buffer, bufferLength );
+
+    if( result == JSONSuccess )
+    {
+        result = JSON_Search( buffer, bufferLength, queryKey, queryKeyLength, '.',
+                              &value, &valueLength );
+    }
+
+    if( result == JSONSuccess )
+    {
+        // The pointer "value" will point to a location in the "buffer".
+        char save = value[ valueLength ];
+        // After saving the character, set it to a null byte for printing.
+        value[ valueLength ] = '\0';
+        // "Found: bar.foo -> xyz" will be printed.
+        printf( "Found: %s -> %s\n", queryKey, value );
+        // Restore the original character.
+        value[ valueLength ] = save;
+    }
+
+    return 0;
+}
+```
+A search may descend through nested objects when the `queryKey` contains matching key strings joined by a separator (e.g. `.`). In the example above, `bar` has the value `{"foo":"xyz"}`. Therefore, a search for query key `bar.foo` would output `xyz`.
+
+## Building coreJSON
+
+A compiler that supports **C89 or later** such as *gcc* is required to build the library.
+
+For instance, if the example above is copied to a file named `example.c`, *gcc* can be used like so:
+```bash
+gcc -I source/include example.c source/core_json.c -o example
+./example
+```
+
+*gcc* can also produce an output file to be linked:
+```bash
+gcc -I source/include -c source/core_json.c
+```
+
+## Generating documentation
+
+The Doxygen references were created using Doxygen version 1.8.20. To generate the
+Doxygen pages, please run the following command from the root of this repository:
+
+```shell
+doxygen docs/doxygen/config.doxyfile
+```
+
+## Building unit tests
+
+### Platform Prerequisites
+
+- For running unit tests
+    - C90 compiler like gcc
+    - CMake 3.13.0 or later
+    - Ruby 2.0.0 or later is additionally required for the CMock test framework (that we use).
+- For running the coverage target, gcov is additionally required.
+
+### Steps to build Unit Tests
+
+1. Go to the root directory of this repository.
+
+1. Create build directory: `mkdir build && cd build`
+
+1. Run *cmake* while inside build directory: `cmake -S ../test `
+
+1. Run this command to build the library and unit tests: `make all`
+
+1. The generated test executables will be present in `build/bin/tests` folder.
+
+1. Run `ctest` to execute all tests and view the test run summary.