Added README documentation for unit tests and fixed typos (#106)

* Fixed minor typos in readme

* Created a README for general unit testing purposes and fixed typo in main.cpp of unittests.

unittests/README.md

@@ -0,0 +1,31 @@
+# Unit Testing
+The correctness of new implementations can be verified via running unit tests. Below are the information on how to run unit tests.
+## Requirements
+### 1. Cassandra cluster
+Have access to a **local (127.0.0.1)** Cassandra cluster, opened at port **9042**. Please ensure that the cluster is successfully running before running Unit Tests.
+### 2. Postgres server
+Have access to a **local (127.0.0.1)** Postgres server, opened at port **5432**. The server must also have a super user named **postgres** with password set to **postgres**. In addition, modify *postgresql.conf* with the following field values:
+```
+max_connections = 1000
+shared_buffers = 1280MB
+```
+## Running
+To run the unit tests, first build Clio as normal, then execute `./clio_tests` to run the unit tests.
+
+## Tests
+Below is a list of currently available unit tests. Please keep in mind that this list should be constantly updated with new unit tests as new features are added to the project.
+
+- BackendTest.basic
+- Backend.cache
+- Backend.cacheBackground
+- Backend.cacheIntegration
+
+# Adding Unit Tests
+To add unit tests, append a new test block in the unittests/main.cpp file with the following format:
+
+```cpp
+TEST(module_name, test_name)
+{
+    // Test code goes here
+}
+```