Add best practice for avoiding native symbol name collisions (dotnet#9484)

* Add best practice for avoiding native symbol name collisions

* Update xml/System.Runtime.InteropServices/UnmanagedCallersOnlyAttribute.xml

Co-authored-by: Aaron Robinson <[email protected]>

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Co-authored-by: Aaron Robinson <[email protected]>

Author: jkotas

xml/System.Runtime.InteropServices/UnmanagedCallersOnlyAttribute.xml

@@ -138,6 +138,7 @@ Supplied types must be from the official <xref:System.Runtime.CompilerServices>
 ## Remarks
 
 The export name must be a valid identifier for a native symbol on the target platform. The identifier must not conflict with system-provided native identifiers (for example, names of methods in the C standard library, or POSIX/Win32 API names).
+Using a prefix for symbols is a common way to avoid name collisions of native symbols. For example, you can name the exported functions as `mylibrary_free`, `mylibrary_isdigit` and `mylibrary_copy` to avoid name collisions.
 
 Target-dependent name mangling will be performed on the symbol name such as prepending or appending `_` or `@` characters to distinguish calling conventions on x86 Windows.