Add clang-format config and update the Contribution doc.

Author: Diptorup Deb

.clang-format

@@ -0,0 +1,25 @@
+BasedOnStyle: LLVM
+IndentWidth: 4
+AccessModifierOffset: -4
+AlignEscapedNewlines: Right
+AllowAllParametersOfDeclarationOnNextLine: false
+BinPackParameters: false
+BreakBeforeBraces: Custom
+BraceWrapping:
+  AfterCaseLabel:  true
+  AfterClass:      true
+  AfterControlStatement: MultiLine
+  AfterEnum:       true
+  AfterFunction:   true
+  AfterNamespace:  true
+  AfterObjCDeclaration: false
+  AfterStruct:     true
+  AfterUnion:      true
+  AfterExternBlock: true
+  BeforeCatch:     false
+  BeforeElse:      true
+  IndentBraces:    false
+  SplitEmptyFunction: true
+  SplitEmptyRecord: true
+  SplitEmptyNamespace: true
+  

CONTRIBUTING.md

@@ -2,6 +2,17 @@
 
 ## Source Code Formatting¶
 
+### C/C++ code style
+
+We use [clang-format](https://clang.llvm.org/docs/ClangFormat.html) code formatter.
+
+Install: `pip install clang`
+
+- Revision: `10.0.1`
+- See the default configuration used by dpCtl in `.clang-format`.
+
+Run before each commit: `clang-format -style=file -i dpctl-capi/include/*.h dpctl-capi/include/Support/*.h dpctl-capi/source/*.cpp dpctl-capi/tests/*.cpp dpctl-capi/helper/include/*.h dpctl-capi/helper/source/*.cpp`
+
 ### Python code style