Import MANIFEST.md for CGRAN's benefit

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

MANIFEST.md

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+title: gr-iqbalance
+brief: GNU Radio block to correct IQ imbalance in quadrature receivers
+tags:
+    - iq imbalance
+    - rx
+    - osmocom
+author:
+    - Sylvain Munaut <tnt@246tNt.com>
+copyright_owner:
+    - Sylvain Munaut <tnt@246tNt.com>
+license: GPLv3
+repo: git://git.osmocom.org/gr-iqbal
+icon: http://people.osmocom.org/~tnt/stuff/iqbal-icon.png
+---
+GNU Radio block to correct IQ imbalance in quadrature receivers
+
+It's composed of two main block:
+ - *fix* : Given a phase and amplitude error, it will correct a complex signal
+ - *optimize*: Attempts to auto-detect the phase and amplitude error to feed to
+   the fix block above
+
+The gr-osmosdr driver can make use of this block automatically if gr-iqbalance
+is installed prior to gr-osmosdr.