add SOLID as a separate chapter

Author: rambasnet

notebooks/00-TableOfContents.ipynb

@@ -21,6 +21,8 @@
     "\n",
     "### [Object-Oriented Design](ObjectOrientedDesign.ipynb)\n",
     "\n",
+    "### [SOLID Principle](SOLID.ipynb)\n",
+    "\n",
     "### [When to Use Object-Oriented Programming](WhenToUseOOP.ipynb)\n",
     "\n",
     "### [Expecting the Unexpected](ExpectingTheUnexpected.ipynb)\n",