Documenting the ENABLE_WASM flag for chrome

The ENABLE_WASM flag was added to www/chromium in 2020[1], but as far
as I know it's never documented, here is my attempt at documenting it.
I found this knob to be often very useful.

If this is the correct approach, I will add the same knob and docs to
iridium and send the diff.

any comments?

related thread:
https://marc.info/?t=154376433600001&r=1&w=2

[1]: https://github.com/openbsd/ports/commit/f0bc9618e1437c8ef2a0f33cc265f9bf08e56f81

diff --git a/www/chromium/Makefile b/www/chromium/Makefile
index b039db54747..2655d58953b 100644
--- a/www/chromium/Makefile
+++ b/www/chromium/Makefile
@@ -7,7 +7,7 @@ DPB_PROPERTIES= parallel parallel2
COMMENT= Chromium browser

V= 102.0.5005.61
-REVISION= 0
+REVISION= 1

DISTNAME= chromium-${V}

diff --git a/www/chromium/pkg/README b/www/chromium/pkg/README
index d543f8fc71b..407cb1c6350 100644
--- a/www/chromium/pkg/README
+++ b/www/chromium/pkg/README
@@ -33,6 +33,17 @@ opening files in /var/www/htdocs directly in chromium), add the paths
to ${SYSCONFDIR}/chromium/unveil.main and merge with changes in files in
${PREFIX}/share/examples/chromium/ at update time.

+WebAssemble:
+- some websites require WebAssemble to be functional, this will appear in
+the JavaScript console as the following error:
+
+ Uncaught (in promise) ReferenceError: WebAssembly is not defined
+
+- WebAssemble is disabled by default due to stability issues, to enable it,
+exit chrome first if it's running then start chrome with ENABLE_WASM defined:
+
+ $ ENABLE_WASM=Yes chrome
+
webgl and 3d and acceleration support:
- some DRM supported cards are marked as unsupported by chromium
Using --ignore-gpu-blacklist may allow you to test