add snapp options documentation

docs/snap-config-options.md

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+
+# snapp config options
+
+## required
+
+### ifname
+network interface name 
+### ifaddr
+ip range of network interface
+
+## optional
+
+### keyfile
+the private key to persist address with.
+if not specified the address will be ephemeral.
+### reachable
+bool value that sets if we publish our snapp to the dht
+`true`: we are reachable via dht
+`false`: we are not reachable via dht
+### hops
+number of hops in a path, min is `1`, max is `8`, defaults to `4`
+### paths
+number of paths to maintain at any given time, defaults to `6`.
+### blacklist-snode
+adds a `.snode` to path build blacklist
+### exit-node
+specify a `.snode` or `.loki` address to use as an exit broker
+### local-dns
+address to bind local dns resoler to, defaults to `127.3.2.1:53`
+if port is omitted it uses port `53`
+### upstream-dns
+address to forward non lokinet related queries to. if not set lokinet dns will reply with srvfail.
+### mapaddr
+perma map `.loki` address to an ip owned by the snapp
+to map `whatever.loki` to `10.0.10.10` it can be specified via:
+```
+mapaddr=whatever.loki:10.0.10.10
+```
+
+## compile time optional features
+
+### on-up
+path to shell script to call when our interface is up
+### on-down
+path to shell script to call when our interface is down
+### on-ready
+path to shell script to call when snapp is first ready