test: Update spectests README

test/spectests/README.md

@@ -3,34 +3,39 @@
 ## Build and run
 
 Fizzy must be built with the `FIZZY_TESTING` option turned on:
-```sh
-$ mkdir build && cd build
-$ cmake -DFIZZY_TESTING=ON ..
-$ cmake --build .
+```shell script
+mkdir build && cd build
+cmake -DFIZZY_TESTING=ON ..
+cmake --build .
 ```
 
 It can then be executed:
-```sh
-$ bin/fizzy-spectests <test directory>
-```
-
-This will execute all test cases, but since Fizzy does not implement the complete validation specification, most of
-those cases will fail. It is possible to skip them:
-```sh
-$ bin/fizzy-spectests --skip-validation <test directory>
+```shell script
+bin/fizzy-spectests <test directory>
 ```
 
 ## Preparing tests
 
 Fizzy uses the official WebAssembly "[spec tests]", albeit not directly.
 It requires the Wast files to be translated into a JSON format using [wabt]'s `wast2json` tool.
 
-The reason for this is a design decision of Fizzy to not support the WebAssembly text format –– and unfortunately
+The reason for this is a design decision of Fizzy to not support the WebAssembly text format, and unfortunately
 the official test cases are in a text format.
 
 In order to prepare the tests, run the following command for each file:
-```sh
-$ wast2json <file.wast> -o <file.json>
+```shell script
+wast2json <file.wast> -o <file.json>
+```
+
+Make sure to disable all WebAssembly extensions when using `wast2json`:
+```shell script
+wast2json --disable-saturating-float-to-int --disable-sign-extension --disable-multi-value
+```
+
+To convert all files at once:
+```shell script
+# Make sure $options here contains the above settings
+find test/core -name '*.wast' -exec wast2json $options {} \;
 ```
 
 For ease of use, we have placed the JSON files of the spec tests [w3c-v1.0 branch] here: