docs build: Document tsc requirement (insofar as we know)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/docs/build.rst b/docs/build.rst
index 15ce23a912197dfac3686209e16b6bd97c139a5a..46fd0e5d8e02dcc13c84b9e8f2b69ee2bd9c0b81 100644 (file)
--- a/docs/build.rst
+++ b/docs/build.rst
@@ -9,7 +9,10 @@ You will need at least 6000 megabytes of disk space, or more, and a
 good internet connection.  Your computer will be compiling a lot of
 code.
 
-These instructions were once tested on Debian buster.
+These instructions were once tested on Debian 10 "buster".  Otter
+won't build on Debian 9 "stretch" because the Typescript compiler
+(tsc) is too old.  tsc 3.3.3333 is known to work.  Ubuntu 20.04LTS
+"focal" should work.
 
 Setup
 -----