Merge #15922: doc: Explain how to pass in non-fundamental types into functions

faede74 doc: Explain how to pass in non-fundamental types into functions (MarcoFalke)

Pull request description:

  There is a common misconception in C++ that one ampersand is better than no ampersand and two ampersands are better than one.

ACKs for commit faede7:
  practicalswift:
    ACK faede74
  jonasschnelli:
    ACK faede74

Tree-SHA512: be12c23287398e4525f16e13de30e51a42d9e38284644eed5b67fa23197b09436d75a3aa8db08555ee91a38a0f159d2722b8a9927ce0bc906e600d2a7976086b

Author: MarcoFalke

doc/developer-notes.md

@@ -478,6 +478,14 @@ Wallet
 General C++
 -------------
 
+For general C++ guidelines, you may refer to the [C++ Core
+Guidelines](https://isocpp.github.io/CppCoreGuidelines/).
+
+Common misconceptions are clarified in those sections:
+
+- Passing (non-)fundamental types in the [C++ Core
+  Guideline](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rf-conventional)
+
 - Assertions should not have side-effects
 
   - *Rationale*: Even though the source code is set to refuse to compile