Adds usage, buid instruction and general info to README

Author: brejoc

README.md

@@ -1,2 +1,23 @@
 # bscdiff
-bscdiff compares bsc, issue and CVE numbers in changelogs
+
+bscdiff compares bsc, issue and CVE numbers from a source changelog, to a target changelog. Missing numbers are then printed with their occurrence in the source changelog.
+
+
+## Usage
+
+```
+brejoc@alpha ~> ./bscdiff source.changes target.changes
+508: bsc#1098394 -> - Fix file.get_diff regression on 2018.3 (bsc#1098394)
+525: bsc#1098394 -> - Fix file.managed binary file utf8 error (bsc#1098394)
+4092: bsc#565656565 -> - uploaded to salt 1.12.0 (bsc#565656565, bsc#676767676)
+4092: bsc#676767676 -> - uploaded to salt 1.12.0 (bsc#565656565, bsc#676767676)
+```
+
+Output is structure like this:
+
+\<line in source.changes\>: \<bsc missing in target.changes\> -> \<line from source.changes\>
+
+
+## Building bscdiff
+
+Since no external dependency was used, you can just do a `go build bscdiff.go`.