Introduce doc/examples/ directory

It contains simple usual setups to get started with osmo-gsm-tester,
such as creating a 4G network using srsLTE or a 2G network using the
osmocom stack (+ ofono modems).

Change-Id: I55d5b1152da201799af21a77ef6c562f97bd94fc
diff --git a/doc/examples/4g_srsLTE/scenarios/mod-srsue-ncarriers@.conf b/doc/examples/4g_srsLTE/scenarios/mod-srsue-ncarriers@.conf
new file mode 100644
index 0000000..bb6409a
--- /dev/null
+++ b/doc/examples/4g_srsLTE/scenarios/mod-srsue-ncarriers@.conf
@@ -0,0 +1,3 @@
+modifiers:
+  modem:
+  - num_carriers: ${param1}