docs: add more document

docs/mistake.md

@@ -0,0 +1,52 @@
+# Some common mistakes
+
+## Bit-width mismatch
+
+That is, the bit-width of the LHS and RHS of an assignment operation are different.
+For example, the following code will result in compile error:
+
+```cpp
+Register <8>    r1;
+Register <16>   r2;
+r1 <= r2; // Error: bit-width mismatch
+```
+
+## Register/Wire passed by value
+
+Register/Wire can be only passed by reference. We forbid
+the copy/move constructor for Register/Wire to avoid misuse.
+
+This may cause some error in the lambda function of a wire.
+
+```cpp
+Register <8> r1;
+Wire <8> w1 = [&]() { return r1; };
+```
+
+To fix this issue, you may return by reference,
+or use + operator to convert the value to bit type.
+
+```cpp
+Register <8> r1;
+Wire <8> w1 = [&]() -> auto & { return r1; };
+Wire <8> w2 = [&]() { return +r1; };
+```
+
+## C-array as member variable
+
+We do not support C-array as member variable for synchronization.
+Our C++ static reflection library do not support parsing
+C-array as member variable currently.
+
+Always use `std::array` instead.
+
+```cpp
+struct NeedToSync {
+    std::array <Register <1>, 8> data;
+    std::array <Wire <1>, 8> data2;
+};
+```
+
+## Some others
+
+If you encounter some other issues, please feel free to open an issue.