doc: Add overview doc for user_docs

This document is converted from Technology page on wiki
https://wiki.flashrom.org/Technology

Change-Id: I93107d6b5530c301dd90f7177758632d9d1810eb
Signed-off-by: Anastasia Klimchuk <aklm@flashrom.org>
---
M doc/intro.rst
A doc/user_docs/Amd_am29f010_tsop32.jpg
A doc/user_docs/Bios_savior.jpg
A doc/user_docs/Dip32_chip.jpg
A doc/user_docs/Dip32_chip_back.jpg
A doc/user_docs/Dip32_in_socket.jpg
A doc/user_docs/Dip8_chip.jpg
A doc/user_docs/Dip8_chip_back.jpg
A doc/user_docs/Dip8_in_socket.jpg
A doc/user_docs/Dip_tool.jpg
A doc/user_docs/Dual_plcc32_soldered.jpg
A doc/user_docs/Empty_dip32_socket.jpg
A doc/user_docs/Empty_dip8_socket.jpg
A doc/user_docs/Empty_plcc32_socket.jpg
A doc/user_docs/Flash-BGA.jpg
A doc/user_docs/Plcc32_chip.jpg
A doc/user_docs/Plcc32_chip_back.jpg
A doc/user_docs/Plcc32_in_socket.jpg
A doc/user_docs/Plcc_tool.jpg
A doc/user_docs/Pushpin_roms_2.jpg
A doc/user_docs/Soic8_chip.jpg
A doc/user_docs/Soic8_socket_back.jpg
A doc/user_docs/Soic8_socket_front_closed.jpg
A doc/user_docs/Soic8_socket_half_opened.jpg
A doc/user_docs/Soic8_socket_open.jpg
A doc/user_docs/Soic8_socket_with_chip.jpg
A doc/user_docs/Soic8_socket_with_chip_inserted.jpg
A doc/user_docs/Soldered_plcc32.jpg
A doc/user_docs/Soldered_tsop40.jpg
A doc/user_docs/Soldered_tsop48.jpg
A doc/user_docs/Spi-socket-dscn2913-1024x768.jpg
A doc/user_docs/Sst_39vf040_tsop32.jpg
A doc/user_docs/Top_hat_flash.jpeg
M doc/user_docs/index.rst
A doc/user_docs/overview.rst
35 files changed, 303 insertions(+), 1 deletion(-)