Added README for tests directory (#2844)

* Added README for tests directory

* Whitespace fix

Author: MatthewDaggitt

tests/README.md

@@ -0,0 +1,32 @@
+Test suite
+==========
+
+Building the library
+####################
+
+You can test the building of the entire library by running the following command from the top-level directory of the library:
+```bash
+cabal run GenerateEverything -- --include-deprecated
+agda -Werror +RTS -M5G -H3.5G -A128M -RTS -i. -isrc -idoc -WnoUserWarning Everything.agda
+```
+
+Golden tests
+############
+
+Setup
+-----
+
+The golden tests need the `clock` package from Cabal to run.
+This can be installed via:
+```bash
+cabal v1-install --ghc-options='-O1 +RTS -M6G -RTS' clock
+```
+
+Running
+-------
+
+The golden tests can be run from the top-level directory of the library with the command:
+```bash
+make testsuite INTERACTIVE='' AGDA_EXEC='~/.cabal/bin/agda'
+```
+This should take about 5 minutes to run.