repo: add initial changelog file

CHANGELOG

+Change Log for Releases
+=======================
+
+## 23.5
+ * Updated ASN.1 of RRC/NGAP/F1AP/E1AP to 3GPP Release 17.4
+ * Add UE capability transfer procedure
+ * Add support for srsUE
+ * CSI-RS in Downlink
+ * Add virtual RF driver to use with Amarisoft UE
+ * Expose further config parameters
+ * Other bug-fixes and improved stability and performance in all parts
+
+## 23.3 (initial public release)
+ * FDD/TDD supported, all FR1 bands
+ * 15/30 KHz subcarrier spacing
+ * All physical channels including PUCCH Format 1 and 2, excluding Sounding-RS
+ * Highly optimized LDPC and Polar encoder/decoder for ARM Neon and x86 AVX2/AVX512
+ * All RRC procedures excluding Mobility, Paging and Reestablishment
+ * All MAC procedures excluding power control
+ * Split 8 support using Ettus/NI USRPs
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