README: Add information about meson and link build instructions

The patch adds one paragraph of information about meson into the
README file. This meant to be the minimum required to unblock
release candidate. README file will have a more substantial
upgrade soon.

Ticket: https://ticket.coreboot.org/issues/354

Original-Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/70176
Original-Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
(cherry picked from commit 80408ceafc2a9a550bb5ef7aabd772dbf5d34487)

Change-Id: I2a27d8f2ba42e18be2485ae95bec1b4c874bb4f7
Signed-off-by: Evan Benn <evanbenn@google.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/70321
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

README

@@ -46,6 +46,18 @@ from the tarball, as controlled by the .gitattributes files.
 Build Instructions
 ------------------
 
+flashrom supports building with make and meson.
+
+Meson build system supports almost all the environments, although not exactly
+all of them. Full meson support is on the roadmap in the nearest future.
+To build flashrom with meson, follow the instruction and information in
+/Documentation/building.md
+
+If you are unsure which build system to use, and/or don't know what's the
+difference, use make for now.
+
+The rest of Build Instructions below refers to building flashrom with make.
+
 To build flashrom you need to install the following software:
 
  * C compiler (GCC / clang)