Adding dependencies and known issues chapter

README.md

@@ -1,3 +1,26 @@
 # readlink
 
-Replicate `readlink -f` as bash script using mainly dependencies available on most bash 3 platforms.
+Replicate `readlink -f` as bash script using mainly dependencies available on most platforms:
+
+* `readlink` (without options)
+* `cd`
+* `pwd -P`
+* `test -e` (as `[ -e <file> ]`)
+
+# Known issues
+
+* When `readlink` is part of a pipe some links contain the current pipe described like `pipe:[123456]` where the number changes on every call.  
+  `readlink` resolves these as valid links.
+
+  e.g.
+  ```
+  $ readlink -f /dev/stdout
+  /dev/pts/0
+
+  $ readlink -f /dev/stdout | cat
+  /proc/737861/fd/pipe:[2332393]
+
+  $ ./rdlink.sh /dev/stdout
+
+  ```
+  Whereas `rdlink` is not able to evaluate such links, because the pipe is already invalid as soon as a expression like `result="$(readlink "${tocheck}")"` returns.