etc/pipewire: document the volume cutoff (pulseaudio style) workaround

etc/pipewire/media-session.d/README.md

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+The old pulseaudio fix for less than 20 % volume being unhearable is editing `alsa-monitor.conf` and uncommenting `api.alsa.ignore-dB = true`
+
+```
+2021-049 11:44:40 EET <@wtay> Mikaela, you can set api.alsa.ignore-dB = true in /etc/pipewire/media-session.d/alsa-monitor.conf
+2021-049 11:45:31 EET <@wtay> Mikaela, or alternatively: api.alsa.soft-mixer = true in alsa-monitor.conf
+```
+
+from #pipewire on freenode which has public logging according to the title.

etc/pipewire/media-session.d/alsa-monitor.conf.example.donotuse

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+# alsa-monitor config file
+properties = {
+    #alsa.jack-device = true
+}
+
+rules = [
+    # an array of matches/actions to evaluate
+    {
+        # rules for matching a device or node. It is an array of
+        # properties that all need to match the regexp. If any of the
+        # matches work, the actions are executed for the object.
+        matches = [
+            {
+	        # this matches all cards
+                device.name = ~alsa_card.*
+            }
+        ]
+        actions = {
+            # actions can update properties on the matched object.
+            update-props = {
+                api.alsa.use-acp = 		true
+                #api.alsa.use-ucm = 		true
+                #api.alsa.soft-mixer = 		true
+                api.alsa.ignore-dB = 		true
+                #device.profile-set = 		"profileset-name"
+                #device.profile = 		"default profile name"
+                api.acp.auto-profile = 		false
+                api.acp.auto-port = 		false
+                #device.nick = 			"My Device"
+            }
+        }
+    }
+    {
+        matches = [
+            {
+	        # matches all sinks
+                node.name = ~alsa_input.*
+            }
+            {
+	        # matches all sources
+                node.name = ~alsa_output.*
+            }
+        ]
+        actions = {
+            update-props = {
+                #node.nick = 			"My Node"
+                #node.nick = 			null
+                #priority.driver = 		100
+                #priority.session = 		100
+                #node.pause-on-idle = 		false
+                #resample.quality = 		4
+                #channelmix.normalize =		false
+                #channelmix.mix-lfe = 		false
+                #audio.channels = 		2
+                #audio.format = 		"S16LE"
+                #audio.rate = 			44100
+                #audio.position = 		"FL,FR"
+                #api.alsa.period-size =         1024
+                #api.alsa.headroom =            0
+                #api.alsa.disable-mmap =        false
+                #api.alsa.disable-batch =       false
+            }
+        }
+    }
+]