README.md: introduce known issue section

The users might run into data corrupted issues caused by underlay filesystem.
It's out of scope for bboltdb maintainers to fix filesystem issue. But
the section to track known issues can help users and contributors to analyse
root cause when they run into data corrupted issues.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

README.md

@@ -69,6 +69,7 @@ New minor versions may add additional features to the API.
     - [LMDB](#lmdb)
   - [Caveats & Limitations](#caveats--limitations)
   - [Reading the Source](#reading-the-source)
+  - [Known Issues](#known-issues)
   - [Other Projects Using Bolt](#other-projects-using-bolt)
 
 ## Getting Started
@@ -934,6 +935,19 @@ The best places to start are the main entry points into Bolt:
 If you have additional notes that could be helpful for others, please submit
 them via pull request.
 
+## Known Issues
+
+- bbolt might run into data corruption issue on Linux when the feature
+  [ext4: fast commit](https://lwn.net/Articles/842385/), which was introduced in
+  linux kernel version v5.10, is enabled. The fixes to the issue were included in
+  linux kernel version v5.17, please refer to links below,
+
+  * [ext4: fast commit may miss tracking unwritten range during ftruncate](https://lore.kernel.org/linux-ext4/20211223032337.5198-3-yinxin.x@bytedance.com/)
+  * [ext4: fast commit may not fallback for ineligible commit](https://lore.kernel.org/lkml/202201091544.W5HHEXAp-lkp@intel.com/T/#ma0768815e4b5f671e9e451d578256ef9a76fe30e)
+  * [ext4 updates for 5.17](https://lore.kernel.org/lkml/YdyxjTFaLWif6BCM@mit.edu/)
+
+  Please also refer to the discussion in https://github.com/etcd-io/bbolt/issues/562.
+
 
 ## Other Projects Using Bolt