PCBNEW: The routing startpoint violates DRC. (Tell me why!)

Description

When a wire cannot be drawn due to drc, a message is shown: "The routing startpoint violates DRC". It would be handy, to know which rule it is. It should be displayed why the line cannot be drawn.

Steps to reproduce

1. DRC is violated
2. Display why.

KiCad Version

Application: Pcbnew

Version: (5.99.0-7910-gdc28de16d4), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.71.0 OpenSSL/1.1.1g (Schannel) zlib/1.2.11 brotli/1.0.7 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.41.0

Platform: Windows 10 (build 10586), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Dec 29 2020 11:16:24
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8)
	Boost: 1.73.0
	OCE: 6.9.1
	Curl: 7.71.0
	ngspice: 32
	Compiler: GCC 10.2.0 with C++ ABI 1014

Build settings:
	KICAD_SCRIPTING=ON
	KICAD_SCRIPTING_MODULES=ON
	KICAD_SCRIPTING_PYTHON3=OFF
	KICAD_SCRIPTING_WXPYTHON=ON
	KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
	KICAD_SCRIPTING_ACTION_MENU=ON
	KICAD_USE_OCE=ON
	KICAD_SPICE=ON