Add Code Guideline draft.

Author: yaroslavyaroslav

CODE GUIDELINE.md

@@ -0,0 +1,49 @@
+# Web3swift code guidelines
+## General
+* Git methodology — gitflow
+* ci/cd must be ran successfully on every merge to develop
+* commits description should be verbose and concrete.
+    * at least each change in file should be described in several words.
+    * No *etc* description allowed.
+* Commit should not confusing by its size or content
+    * If you’re adding or deleting a large amount of files you’ve should do it in separate commit, which will not include any code written by you.
+    * If you’re renaming some type or do any other action that affects a large amount of source files do it as separate commit with such description `Rename ExampleType to AnotherExampleType`.
+    * If you’re task is big enough, like, if it’s affecting 20+ source files where you’ll should to write your code, please, split it in separate commits that will affect less than 10 files at each. 
+
+## CI/CD
+CI/CD including follow checks:
+- `swiftlint` with the ruleset which stores in `.swiftlint.yml` must produces no errors or warnings.
+- compiling as library (on each supported platform)
+    - Carthage
+    - CocoaPods
+    - Swift Package Manager 5.4
+- compiling as dependency (on each supported platform)
+    - Carthage
+    - CocoaPods
+    - Swift Package Manager 5.4
+- All test should be green.
+
+## General Code requirements
+### Active development
+- No rules for code quality applies while active development is going on.
+
+### Merge to `develop`
+- there’s shouldn’t have any commented out code in the library itself, but could be in Tests target.
+- there’s should run CI/CD pipeline successfully.
+- building the library should produce no warnings on both stages
+    - no package manager warnings (Carthage, SPM, CocoaPods)
+    - no target building warnings
+
+## Swift code formatting requirements
+### Active development
+- No rules for code quality applies while active development is going on.
+
+### Merge to `develop`
+- if you’re not 100% sure that this is required there’s shouldn’t be any `#if DEBUG` clauses in the code.
+- All required logs should be produced by `os_log()` method, not `print()` one.
+    - all logs message should have clear descriptions.
+- `try` clause should should be used to return optional value, not trows and error at most, that is could be called without `do { } catch { }` block. You’re able to use block above, but it should be required there, for example, there’s should be error handling code in `catch`.
+- force optional try (`let someVar = try! someTrhowableMethod()`) are not allowed.
+- there’s shouldn’t be any unsafe force unwrap (`let someVar = optionalVar!` at all. But you could use such case as `if !array.isEmpty, let element = array.first! { }`.
+- All string types identifiers, like `if object.name == "someName" { }` should be strong typed as enum `if object.name = ExampleEnum.someName.rawValue`
+- Newly added methods should be followed with its description by the Xcode builtin tools (`cmd+option+/`).