[ bug ] `README` text

[jamesmckinna]

Issue #1743 and its closing PR #2184 missed updating the following text:

agda-stdlib/doc/README.agda

Lines 289 to 292 in 99167f7

	-- Note that all library sources are located under src or ffi. The
	-- modules README, README.* and Everything are not really part of the
	-- library, so these modules are located in the top-level directory
	-- instead.

which should (since v2.0!) instead read:

-- Note that all library sources are located under src or ffi. The
-- modules README, README.* and Everything are not really part of the
-- library, so these modules are located in the doc directory instead.